By mixing his colours with white, the artist obtains his tints. By mixing colours with colours, he produces compound colours, or hues. And by mixing colours or tints with black, he gets shades. It is a common error to confound these distinctions.

The above classification of colours enables us to understand the simplicity of relation which exists among an infinity of tints, hues, and shades of colour. Also, it is calculated to give precision to language respecting colours, the nomenclature of which has too often been vague and uncertain.

There are five classes of colours, viz.:—the Neutral, the Primary, the Secondary, the Tertiary, and the Semi-neutral.

Neutral Colours are three only, white, black, and grey. According to the laws of Optics, the two first comprise all other colours synthetically, and afford them all by analysis. These are sometimes called "extreme" colours, grey being their intermediate.

Primary Colours are three only, yellow, red, and blue. They are such as yield others by being compounded, but are not themselves capable of being produced by composition of other colours. By way of distinction, they are occasionally designated "entire" colours.

Secondary Colours, are three only, orange, green, and purple. Each of these is composed of, or can be resolved into, two primaries. Thus, orange is composed of red and yellow; green, of yellow and blue; and purple, of blue and red.

Tertiary Colours are three only, citrine, russet, and olive. Each of these is composed of, or can be resolved into, either two secondary colours, or the three primaries. Thus, citrine consists of green and orange, or of a predominant yellow with blue and red; russet is compounded of orange and purple, or of a predominant red with blue and yellow; and olive is composed of purple and green, or of a predominant blue with yellow and red.

The last three genera of colours comprehend in an orderly gradation all those which are positive or definite; and the three colours of each genus, united or compounded in such subordination that neither of them predominates to the eye, constitute the negative or neutral colours, of which black and white have been stated to be the opposed extremes, and greys their intermediates. Thus black and white are constituted of, and comprise latently, the principles of all colours, and accompany them in their depth and brilliancy as shade and light.

Semi-neutral Colours belong to a class of which brown, marrone, and gray may be considered types. They are so called, because they comprehend all the combinations of the primary, secondary, and tertiary colours, with the neutral black. Of the various combinations of black, those in which yellow, orange, or citrine predominates, have obtained the name of brown, &c. A second class in which the compounds of black are of a predominant red, purple, or russet hue, comprises marrone, chocolate, &c. And a third class, in which the combinations of black have a predominating hue of blue, green, or olive, includes gray, slate, &c.

While treating of the classes of colours, it may not be out of place to note here the difference between gray as spelt with an a, and grey as spelt with an e, the two names being occasionally confounded. Gray is semi-neutral, and denotes a class of cool cinereous colours, faint of hue; whence we have blue grays, olive grays, green grays, purple grays, and grays of all hues in which blue predominates; but no yellow or red grays, the predominance of such hues carrying the compounds into the classes of brown and marrone, of which gray is the natural opposite. Grey is neutral, and is composed of or can be resolved into black and white alone, from a mixture of which two colours it springs in an infinite series.

It must be observed that each colour may comprehend an indefinite series of shades between the extremes of light and dark, as each compound colour also may comprise a similar series of hues between the extremes of the colours composing it. And as the relations of colours have been deduced regularly, from white or light to black or shade; so the same may be done, inversely, from black to white. On this plan the tertiaries, olive, russet, and citrine, take the place of the primaries, blue, red, and yellow; while the secondaries still retain their intermediate station and relation to both.

Thus, russet and olive compose or unite in dark purple; citrine and olive in dark green; russet and citrine in dark orange. The tertiaries have, therefore, the same order of relation to black that the primaries have to white; and we have black primaries, secondaries, and tertiaries, inversely, as we have white primaries, secondaries, and tertiaries, directly. In other words, we have light and dark colours in all classes.