130. Reflected Light. _Opaque Objects._ In Section 106 we learned
that most objects are visible to us because of the light diffusely
reflected from them. A white object, such as a sheet of paper, a
whitewashed fence, or a table cloth, absorbs little of the light which
falls upon it, but reflects nearly all, thus producing the sensation
of white. A red carpet absorbs the light rays incident upon it except
the red rays, and these it reflects to the eye.

Any substance or object which reflects none of the rays which fall
upon it, but absorbs all, appears black; no rays reach the eye, and
there is an absence of any color sensation. Coal and tar and soot are
good illustrations of objects which absorb all the light which falls
upon them.

131. How and Why Colors Change. _Matching Colors._ Most women prefer
to shop in the morning and early afternoon when the sunlight
illuminates shops and factories, and when gas and electricity do not
throw their spell over colors. Practically all people know that
ribbons and ties, trimmings and dresses, frequently look different at
night from what they do in the daytime. It is not safe to match colors
by artificial light; cloth which looks red by night may be almost
purple by day. Indeed, the color of an object depends upon the color
of the light which falls upon it. Strange sights are seen on the
Fourth of July when variously colored fireworks are blazing. The child
with a white blouse appears first red, then blue, then green,
according as his powders burn red, blue, or green. The face of the
child changes from its normal healthy hue to a brilliant red and then
to ghastly shades.

Suppose, for example, that a white hat is held at the red end of the
spectrum or in any red light. The characteristics of white objects is
their ability to reflect _all_ the various rays that fall upon them.
Here, however, the only light which falls upon the white hat is red
light, hence the only light which the hat has to reflect is red light
and the hat consequently appears red. Similarly, if a white hat is
placed in a blue light, it will reflect all the light which falls upon
it, namely, blue light, and will appear blue. If a red hat is held in
a red light, it is seen in its proper color. If a red hat is held in a
blue light, it appears black; it cannot reflect any of the blue light
because that is all absorbed and there is no red light to reflect.

A child wearing a green frock on Independence Day seems at