es, such as
yellow and green, green and blue, blue and purple, or purple and red.
Next let us think of the result of mixing different values in opposite
hues; as, for instance, YR7 and B3 (Fig. 11). To this combination the
color sphere gives a ready answer; for the middle of a straight line
through the sphere, and joining them, coincides with the neutral centre,
showing that they _balance in neutral gray_. This is also true of any
opposite pair of surface hues where the values are equally removed from
the equator.

[Illustration: Fig. 11.]

(73) Suppose we substitute familiar flowers for the notation, then YR7
becomes the buttercup, and B3 is the wild violet. But, in comparing the
two, the eye is more stimulated by the buttercup than by the violet, not
alone because it is lighter, but because it is stronger in chroma; that
is, farther away from the neutral axis of the sphere, and in fact out
beyond its surface, as shown in Fig. 11.

The head of a pin stuck in toward the axis on the 7th level of YR may
represent the 9th step in the scale of chroma, such as the buttercup,
while the "modest" violet with a chroma of only 4, is shown by its
position to be nearer the neutral axis than the brilliant buttercup by
five steps of chroma. This is the third dimension of color, and must be
included in our notation. So we write the buttercup YR 7/9 and the
violet B 3/4,--chroma always being written below to the right of hue,
and value always above. (This is the invariable order: HUE
{VALUE/CHROMA}.)

(74) A line joining the head of the pin mentioned above with B 3/4 does
not pass through the centre of the sphere, and its middle point is
nearer the buttercup than the neutral axis, showing that the hues of the
buttercup and violet _do not balance in gray_.

+The neutral centre is a balancing point for colors.+

(75) This raises the question, What is balance of color? Artists
criticise the color schemes of paintings as being "too light or too
dark" (unbalanced in value), "too weak or too strong" (unbalanced in
chroma), and "too hot or too cold" (unbalanced in hue), showing that
this is a fundamental idea underlying all color arrangements.

(76) Let us assume that the centre of the sphere is the natural
balancing point for all colors (which will be best shown by Maxwell
discs in Chapter V., paragraphs 106-112), then color points equally
removed from the centre must balance one another. Thus white balances
black. Lighter red b