The Munsell Color System
In describing the dimension known as Chroma, we noted the fact that certain of the Hues were much more powerful than others, in this regard, and were represented by lines or paths extending beyond the others and outside of the sphere. We found that Red, for example, on any step of Value is more powerful and requires a longer path than its opposite, complementary, Blue-Green. Yellow, on the other hand, is longer than its opposite, complementary, Purple-Blue, on the high steps of Value, but shorter on the lower steps of Value. This brings us naturally to the question of Balance of Color, the vital question in all practical applications of color. Now if we mixed equal parts of Red at its maximum Chroma with its opposite, Blue-Green, at its maximum, we would not get a perfectly neutral gray, but one in which the Red was decidedly predominate. It would be somewhat like a tug-of-war in which there were 10 men on one side, each representing a step of Chroma, and only 5 on the other. The resulting color would be pulled well over to the Red side, because, as already stated, Red at its maximum Chroma is so much stronger than Blue-Green at its maximum Chroma. If, however, instead of taking equal amounts of the two colors, we took what would correspond to an equal number of steps upon the scale of Chroma, we would find that they do balance and produce a perfectly neutral gray, in which neither the one Hue nor the other predominates.
Let us glance for a moment at the above two diagrams, in which a bar represents the line of Red and Blue-Green, with 5 steps of Chroma for Blue-Green and 10 steps of Chroma for Red, as is the case at middle Value for these two Hues. The bar rests upon a fulcrum at the neutral point and it obviously will not balance, but will fall to the Red side, as in Figure 1. But if we were to cut off steps 6, 7, 8, 9 and 10 from the Red side of the bar, it would balance upon the neutral gray, as in Figure 2. This will likely strike the reader as so simple and obvious that it scarcely merits explanation; but it is just this simplicity which is characteristic of the Munsell Color System throughout, if approached from the same point of view.
This, too, explains why the diameter of our Color Sphere is limited to the shortest Chroma path (5) at Middle Value. It is apparent that within a sphere thus limited, all opposite colors will balance because, since they are all of equal length at each level of Value, no Chroma path can be longer than another or outbalance it.
By using this system, two opposite colors will be balanced by using only equal Chroma steps of each color on the same level of Value, that G 5/3 will balance R-P 5/3 and R 5/5 will balance B-G 5/5
and so on throughout all of the Hues. But in practice we may wish to employ a weak Chroma of one Hue with a strong Chroma of its opposite. In this case we cannot simply chop off the excess strength of color on one end of the line, but must attain the desired Balance by another means. If our purpose is merely to make a perfect gray, we would use a greater amount of the weaker color. But if we want to produce a balanced or harmonious color design, we would use a larger area of the weaker color than of the stronger. If we do this in correct proportions, relative to the strength of Chroma in each of the colors, we will achieve Balance. We may prove that we have achieved Balance by the fact that everything in our design, thus apportioned as to area and strength of Chroma, if mixed together, * would produce a perfect gray. Let us suppose, for example, that in our design we want to use the maximum of Red and Blue-Green at Middle Value. Since we are speaking of Balance, a pair of scales is an apt figure with which to illustrate the point.
We will put five blocks of Red 5/10, its maximum Chroma, into the pan on one side. In order to balance this we must put ten blocks of the strongest Blue-Green, which is only 5/5, into the other pan.
Thus we find that, in order to balance two colors with unequal Chroma but with the same Value, we use a larger area of the weaker Chroma with a lesser area of the stronger. The proportions are simply in inverse ratio to the strength of Chroma of each. That is, we use ten parts of Blue-Green at /5 Chroma with five parts of Red at /10 Chroma, or let us say six parts of Yellow-Red 3/4 with four parts of Blue 3/6, etc.
Thus far we have considered only Balance of opposite Hues on the same level of Value; but more often than not we will want to print a design in colors which are not only different in Chroma strength but also on different levels of Value. This difference of Value will also affect the question of Balance and of the amount of area which each color should occupy in order to attain it. Let us assume that we wish to print a design in Yellow of a high Value and strong Chroma, say Y 7/9, with its opposite, Purple-Blue, at low Value and weak Chroma, say P-B 3/4. The path formed by a line drawn between these colors, passing through the neutral pole would not be horizontal, since they are at different levels of Value, but would appear as in this diagram.
To arrive at a perfectly balanced color design, we now have to take the Value into account in determining the amount of area of each of these two colors to be used. This is done by the simple process of multiplying the Chroma by the Value of each of the colors. Multiplying the Chroma by the Value of Yellow 7/9, 7x9 = 63, and doing the same with Purple-Blue 3/4, 3x4=12, we get these two products 63 and 12. These are applied inversely, as in the former case. We would use 63 parts of Purple-Blue 3/4 with 12 parts of Yellow 7/9. The conclusion is that the stronger Chroma and higher Value should occupy the lesser area and the weaker Chroma and lower Value should occupy the greater area.
It is not to be assumed that in printing a complicated color design the areas could all be measured and made to conform strictly to this law; or that the effect would necessarily be inharmonious if they did not. This is merely a guiding principle or ideal point at which we may aim in the actual printing of a color design. If we had such a design to print in two colors, for example, and one of the blocks from which we were to print it occupied what we would estimate by eye to be about twice as much surface or area as the other block, it would be a simple matter to choose colors to which would work. We might use Purple 4/6 for the larger area and Green-Yellow 6/8 for the smaller. Or we could use Blue 2/3 for the larger and Yellow-Red 3/4 for the smaller, or any other colors which would give us a proportion approximating that of the difference between the areas of our design. Circumstances will often not permit a strict adherence to the proportions indicated by this formula; but it will rarely, if ever, be impossible to follow the general principle of printing the larger area in the lower Value and weaker Chroma and the smaller area in the higher Value and stronger Chroma.
For purposes of illustration we have considered only designs in two colors; but, obviously, the same rule would apply to three or any other number of colors.
*On Maxwell discs.