+Every color can be recognized, named, matched, imitated, and written by its HUE, VALUE, and CHROMA.+ (40) The notation used in this system places Hue (expressed by an initial) at the left; Value (expressed by a number) at the right and above a line; and Chroma (also expressed by a number) at the right, below the line. Thus R 5/9 means HUE (red), VALUE (5)/CHROMA (9), and will be found to represent the qualities of the pigment vermilion.[14] [Footnote 14: See Chapter VI.] Hue, value, and chroma unite in every color sensation, but the child cannot grasp them all at once. _Hue-difference appeals to him first_, and he gains a permanent idea of five principal hues from the enamels of MIDDLE COLORS, learning to name, match, imitate, and finally write them by their initials: R (red), Y (yellow), G (green), B (blue), and P (purple). Intermediates formed by uniting successive pairs are also written by the joined initials, YR (yellow-red), GY (green-yellow), BG (blue-green), PB (purple-blue), and RP (red-purple). (41) Ten differences of hue are as many as a child can render at the outset, yet in matching and imitating them he becomes aware of their light and dark quality, and learns to separate it from hue as _value-difference_. Middle colors, as implied by that name, stand midway between white and black,--that is, on the equator of the sphere,--so that a middle red will be written R 5/, suggesting the steps 6, 7, 8, and 9 which are above the equator, while steps 4, 3, 2, and 1 are below. It is well to show only three values of a color at first; for instance, the middle value contrasted with a light and a dark one. These are written R 3/, R 5/, R 7/. Soon he perceives and can imitate finer differences, and the red scale may be written entire, as R 1/, R 2/, R 3/, R 4/, R 5/, R 6/, R 7/, R 8/, R 9/, with black as 0 and white as 10. (42) _Chroma-difference is the third_ and most subtle color quality. The child is already unconsciously familiar with the middle chroma of red, having had the enamels of MIDDLE COLOR always in view, and the red enamel is to be contrasted with the strongest and weakest red chromas obtainable. These he writes R /1, R /5, R /9, seeing that this describes the chromas of red, but leaves out its values. R 5/1, R 5/5, R 5/9, is the complete statement, showing that, while both hue and value are unchanged, the chroma passes from grayish red to middle red (enamel first learned) and out to the strongest red in the chroma scale obtained by vermilion. (43) It may be long before he can imitate the intervening steps of chroma, many children finding it difficult to express more than five steps of the chroma scale, although easily making ten steps of value and from twenty to thirty-five steps of hue. This interesting feature is of psychologic value, and has been followed in the color tree and color sphere. +Does such a scientific scheme leave any outlet for feeling and personal expression of beauty?+