(35) Such models set up a permanent image of color relations. Every point is self-described by its place in the united scales of hue, value, and chroma. These scales fix each new perception of color in the child’s mind by its situation in the color solid. The importance of such a definite image can hardly be overestimated, for without it one color sensation tends to efface another. When the child looks at a color, and has no basis of comparison, it soon leaves a vague memory that cannot be described. These models, on the contrary, lead to an intelligent estimate of each color in terms of its hue, its value, and its chroma; while the permanent enamels correct any personal bias by a definite standard. (36) Thus defined, a color falls into logical relation with all other colors in the system, and is easily memorized, so that its image may be recalled at any distance of time or place by the notation. (37) These solid models help to memorize and assemble colors and the memory is further strengthened by a simple NOTATION, which records each color so that it cannot be mistaken for any other. By these written scales a child gains an instinctive estimate of relations, so that, when he is delighted with a new color combination, its proportions are noted and understood. (38) Musical art has long enjoyed the advantages of a definite scale and notation. Should not the art of coloring gain by similar definition? The musical scale is not left to personal whim, nor does it change from day to day; and something as clear and stable would be an advantage in training the color sense. (39) Perception of color is crude at first. The child sees only the most obvious distinctions, and prefers the strongest stimulation. But perception soon becomes refined by exercise, and, when a child tries to imitate the subtle colors of nature with paints, he begins to realize that the strongest colors are not the most beautiful,--rather the tempered ones, which may be compared to the moderate sounds in music. To describe these tempered colors, he must estimate their hue, value, and chroma, and be able to describe in what degree his copy departs from the natural color. And, with this gain in perception and imitation of natural color, he finds a strong desire to invent combinations to please his fancy. Thus the study divides into three related attitudes, which may be called recognition, imitation, and invention. Recognition of color is fundamental, but it would be tedious to spend a year or two in formal and dry exercises to train recognition of color alone; for each step in recognition of color is best tested by exercise in its imitation and arrangement. When perception becomes keener, emphasis can be placed on imitation of the colors found in art and in nature, resting finally on the selection and grouping of colors for design.[13] [Footnote 13: See Course of Study, Part II.]