(Lat. color), a property inherent in light, by which, according to its various proportions or quantities, or from some other cause, it excites different vibrations in the optic nerve, which, propagated to the sensorium, affect the mind with different sensations. See CHROMATICS, and OPTICS.
in Heraldry. The colours generally used in heraldry are red, blue, black, green, and purple; technically called gules, azure, sable, vert or sinople, and purpure. Tenne or tawny, and sanguine, are less common. Yellow and white again, called or and argent, are metals, not colours. The metals and colours are sometimes expressed in blazonry by the names of precious stones, or by those of planets or stars. See HERALDRY.
in the Human Species, difference of. See COMPLEXION; AMERICA, vol. ii., p. 677; MAN.
in Painting, is applied both to the drugs and to the tints produced by those drugs, variously mixed and applied. The principal colours used by painters are red and white lead, yellow and red ochres, several kinds of earth, umber, orpiment, lamp black, ivory black, black lead, vermillion, gamboge, lacca or lake, blue and green ashes, verdigris, bistre, raw and burnt sienna, bice, smalt, carmine, ultramarine. For much interesting information regarding the pigments employed by the Greeks and Romans, the reader may consult Vitruvius, vii.; Pliny, xxxiii., xxxiv., xxxv.; Dioscorides, v.; and Theophrastus, De Lapidibus. See also Philosoph. Trans. of Royal Soc., 1815, for the experiments and observations of Sir Humphry Davy on some ancient colours and paintings in the baths of Titus and of Livia, &c.
in Plants, is an attribute found to be very variable. Different colours are observed, not only in different individuals of the same species, but likewise in different parts of the same individual. Thus, marvel of Peru and sweet-william have frequently petals of different colours on the same plant. Three or four different colours are frequently found upon the same leaf or flower, as on the leaves of the amaranthus tricolor, and the flowers of the tulip, auricula, three-coloured violet, and others. To produce the most beautiful and striking variety of colours in such flowers, is the principal delight and business of the florist.
The vegetable colours, and their intermediate shades or gradations enumerated by botanists, are as follow:
- Water-colour, hyalinus. - White, albus. - Lead-colour, cinereus. - Black, niger. - Brown, fuscus. - Pitch-black, ater. - Yellow, luteus. - Straw-colour, flaveus. - Flame-colour, fulves. - Iron-colour, gilvus. - Red. - Flesh-colour, incarnatus. - Scarlet, cocineus. - Purple. - Violet-colour, coruleo-purpureus. - Blue, caeruleus. - Green, viridis.
These colours seem to be appropriated to particular parts of the plant. Thus, white is most common in roots, berries, and the petals of spring flowers; black in the roots and seeds, but rarely in the seed vessel, and scarcely ever in the petals. Yellow is frequent in the antherae, or tops of the stamens; as likewise in the petals of autumnal flowers, and the compound ligulated flowers of Linnaeus. Red is common in the petals of summer flowers, and in the acid fruits; blue and violet-colour in the petals; and green in the leaves and calyx, but rarely in the petals. In the interchanging of colours, which in plants is found to depend upon differences in heat, climate, soil, and culture, a sort of elective attraction is observed to take place. Thus, red is more easily changed into white and blue, blue into white and yellow, yellow into white, and white into purple. A red colour is often changed into a white, in the flowers of heath, mother of thyme, betony, pink, viscous campion, cucubalus, trefoil, orchis, fox-glove, thistle, cudweed, saw-wort, rose, poppy, fumitory, and geranium. Red passes into blue in pimpernel. Blue is changed into white in bell-flower, Greek-valerian, bind-weed, cumbbine, violet vetch, milkwort, goat's rue, viper's bugloss, comfrey, borage, hyssop, dragon's head, scabious, blue-bottle, and succory; but it is changed into yellow in crocus. Yellow passes easily into white in melilot, agrimony, mullein, tulip, bladderia or moth-mullein, and corn marigold. White is changed into purple in wood-sorrel, thorn-apple, peas, and daisy.
Although plants are sometimes observed to change their colour upon being moistened with coloured juices, yet that quality in vegetables seems not so much owing to the nature of their nourishment as to the action of the internal and external air, heat, light, and the primitive organization of the parts. In support of this opinion it may be observed, that there is far less variety in the colours of roots than of the other parts of the plants; the pulp within the skin being usually white, sometimes yellow, rarely red. That this effect is produced by their small intercourse with the external air, appears from the circumstance, that the upper parts of roots, when they happen to stand naked above the ground, are often dyed with several colours. Thus the tops of sorrel roots turn red; those of turnips, mullein, and radishes, become purple; and many others are converted into green, whilst those parts of the same roots which lie more under ground are commonly white. The green colour is so proper to leaves, that many, as those of sage, the young sprouts of St John's wort, and others which are reddish when in the bud, acquire a perfect green upon being fully expanded. In like manner, the leaves of the seaside grape (polygonum), which when young are entirely red, become, as they advance in growth, perfectly green; except the middle and transverse ribs, which retain their former colour.
As flowers gradually open and are exposed to the air, they throw off their old colour and acquire a new one; in fact, no flower has its proper colour until it is fully expanded. Thus the purple stock-julflowers are white or pale in the bud; and in like manner bachelor's buttons, blue-bottle, poppy, red daisies, and many other flowers, though of divers colours when blown, are all white in the bud. Nay, many flowers change their colour thrice successively. Thus, the very young buds of lady's looking-glass, bugloss, and the like, are all white; the larger buds purple or murrey; and the open flowers blue.
With respect to the colours of the juices of plants it may be observed, that most resinous gums are tinctured; some, however, are limpid; and that which drops from the domestic pine is clear as rock-water. The milk of some plants is pale, as in burdock; of others white, as in dandelion, euphorbium, and scorzonera; and of others yellow, as in lovage, and greater celandine. Most mucilages have little colour, taste, or smell. Of all the colours above enumerated, green is the most common to plants, and black the most rare.
Colour, being a quality in plants so apt to change, ought never to be employed in distinguishing their species. These ought to be characterized from circumstances not liable to alteration by culture or other accidents. The same inconstancy of colour observed in the flowers, is likewise to be Colour, found in the other parts of plants. Berries frequently change from green to red, and from red to white. Even in ripe fruits, the colour, whether white, red, or blue, is apt to vary; particularly in apple, pear, plum, and cherry trees. Seeds are more constant in point of colour than the vessel which contains them. In the seeds, however, of the poppy, oats, pea, bean, and kidney-bean, variations are frequently observed. The root, too, although not remarkably subject to change, is found to vary in some species of carrot and radish. Leaves frequently become spotted, as in a species of orchis, hawk-weed, ranunculus, knot-grass, and lettuce; but seldom relinquish their green colour altogether. Those of some species of amaranthus, or flower-gentle, are beautifully coloured. The spots which appear on the surface of the leaves are of different colours, liable to vary, and not unfrequently disappear altogether. The leaves of officinal lungwort, and some species of sow-bread, sorrel, trefoil, and ranunculus, are covered with white spots; those of dog's-tooth violet, with purple and white; those of several species of ranunculus and orchis, with black and purple; those of amaranthus tricolor, with green, red, and yellow; those of ranunculus acris, and a species of bog bean, with red or purple. The under surface of the leaves of some species of pimpernel and the sea-plantain is marked with a number of dots or points; a white line runs through the leaves of Indian reed, black-berried heath, and a species of Canary grass; and the margin or brim of the leaf, in some species of box, honeysuckle, ground ivy, and the evergreen oak, is of a silver-white colour. The whole plant is often found to assume a colour that is unnatural or foreign to it. The varieties in some species of eryngo, mugwort, orach, amaranthus, purslane, and lettuce, furnish examples of this.
Such being the inconstancy of colours in all the parts of the plant, specific names derived from that quality are very properly deemed erroneous by Linnæus; whether they respect the colour of the flower, fruit, seeds, roots, leaves, or express in general the beauty or deformity of the entire plant, with a particular view to that circumstance. But of this impropriety, committed by former botanists, Linnæus himself is not always guiltless. Thus the two species of *sarracena*, or the side-saddle flower, are distinguished by the colour of their petals into the yellow and purple *sarracena*; although the shapes and figure of the leaves afford much more constant as well as striking characters. The same may be said of his *Lupinus albus* and *luteus*; *Reseda alba*, glaucæ, and *lutea*; *Angelica atropurpurea*; *Dictamnus albus*; *Lamium album*; *Selago coccinea*; *Sida alba*; *Passiflora rubra*, *lutea*, *incarnata*, and *carrula*; and of many others, in which the specific name is derived from a character or quality that is so liable to vary in the same species.
In conclusion, of all sensible qualities, colour is the least useful in indicating the virtues and powers of vegetables. The following general positions on this subject are laid down by Linnæus, and seem sufficiently confirmed by experiment.—A yellow colour generally indicates a bitter taste; as in gentian, aloe, celandine, turmeric, and other yellow flowers. Red indicates an acid or sour taste; as in cranberries, barberries, currants, raspberries, mulberries, cherries, the fruit of the rose, sea-buckthorn, and service-tree. Herbs which turn red towards autumn have likewise a sour taste; as sorrel, wood-sorrel, and bloody-dock. Green indicates a crude alkaline taste, as in leaves and unripe fruits. A pale colour denotes an insipid taste; as in endive, asparagus, and lettuce. White promises a sweet luscious taste; as in white currants and plums, sweet apples, &c. Lastly, black indicates a harsh, nauseous disagreeable taste; as in the berries of deadly night-shade, myrtle-leaved sumach, herb-Christopher, and others—many of which are not only unpleasant to the taste, but pernicious and deadly in their effects.
**COLOURS.**
_Incapacity of distinguishing._ This peculiarity of vision was till lately supposed to be a very rare phenomenon. It appears first to have attracted attention in England, and some imperfectly described cases were recorded in the *Phil. Trans.* in the latter half of the preceding century. These examples were supposed to be unique, till the great chemist John Dalton announced himself in 1794 as exhibiting the peculiarity under notice, and described the cases of more than twenty persons similarly circumstanced. Later researches in England, France, Switzerland, Germany, Belgium, and America, have shown that this condition of vision is far from uncommon. Various names have been proposed for it, such as *Daltonism* from Dalton (an objectionable appellation which English writers all decline to use), *achromatopsia*, *dyschromatopsia*, *chromatopsedepsy*, &c. The most convenient English name is that of *colour-blindness*, suggested by Sir David Brewster, which, though not strictly accurate, is sufficiently distinctive to warrant its use even as a scientific term.
Colour-blindness is of two kinds. The one which is exceedingly rare is characterized by an inability to perceive any colour properly so called, the eye being only conscious of black and white, or rather of a very dark, and a very light gray. Living examples of this extreme colour-blindness have been recently described by English and foreign writers.
The other kind of colour-blindness, which is very common, shows itself in an inability to distinguish certain colours from each other, and to distinguish the very light tints of all colours from white, and the very dark shades from black. Those who err thus generally see in the rainbow only two colours, blue and yellow, but in the prismatic solar spectrum, looked at from a short distance, several additional coloured bands are distinguished.
The colours most liable to be confounded with each other are, 1. Red full and bright, including crimson, scarlet and the redder shades of orange, with full and bright green. 2. Brown, including dull red, with dark or dull green. 3. Purple, including pink, crimson, lilac, lavender, and other mixtures of red and blue throughout nearly all their shades, with blue. 4. Green with blue, even by daylight—the most common probably of all the forms of colour-blindness. 5. Red (including crimson and scarlet), with black. 6. Light tints of all colours, such as straw colour, and the equally pale shades of pink, blue, green, &c., with white. 7. Dark shades of all colours, such as claret, purple, olive-blue, with black. Popular interest has been chiefly excited by the mistakes of colour-blind persons between red and green; but in a scientific point of view the most singular mistake is that of full red for black, inasmuch as it implies that the eye thus deceived not only does not see red as red, but does not see it as any colour, or as in any way visible at all. Red light is thus equivalent to no light, and does not make even a luminous impression on the retina. The colour best distinguished by the colour-blind is yellow, and other colours are rarely mistaken for it. Blue, when pure and bright, is also perfectly distinguished, but purples and greens are often mistaken for blue.
Colour-blindness is greatly more common among males than females, but the relative proportion of cases in the two sexes has not been ascertained. Among males there is reason to believe that 1 in 20 is colour-blind in some degree; and that 1 in 50 is colour-blind to the extent of mistaking for each other the colours in the preceding list.
Colour-blindness, when marked, generally shows itself in more than one member of the same family, and has been traced from parent to child, through as many as five generations. It seldom, however, includes all the members of a family, and the whole of the females of a generation often escape. The eyes of the colour-blind present in general no peculiarity in appearance or internal structure, and the power of vision in reference to everything but colour is per- feetly normal, and often appears even superior to that of those who do not mistake colours.
The cause of colour-blindness is not known, but the great majority of authors on the subject are agreed in referring it to some peculiarity of structure in the retina or brain. It appears to be quite incurable, but some assistance in distinguishing colours is derived from the substitution of artificial light for daylight; and yellow spectacles have proved of some service by day.
The subject is of practical importance from the great extent to which coloured signals are employed on railways and at sea; but especially on the former, where the colours preferred, viz., red and green, are among the greatest stumbling blocks of the colour-blind.
The fullest account of this peculiarity of vision will be found in the papers of Professor E. Wartmann of Geneva, the first of which was published in French in 1840, and translated into English in 1846, in Taylor's Scientific Memoirs for that year; the second entitled Deuxieme Mémoire sur le Dottonisme, &c., is published in the Memoires lus à la Société de Physique de Genève, 1849. Some account of it is given in Mr W. Cooper's article Vision in the Cyclopaedia of Anatomy. The latest English researches on the subject are contained in a series of papers by Dr George Wilson in the Edinburgh Monthly Journal of Medical Science for 1853-54.