They should be white; and when papered, it should be with light-colored paper.
Why does dark-colored paper darken a room?
Because it absorbs some of the rays of light which come in at the windows; hence, there is less light in the room. Dark-colored carpets, or dark furniture, darken the room for the same reason.
Does the light from a burning body differ from sun-light?
Yes; it differs in intensity, in color, and in many other ways.
What effect does the lamp-light have upon the color of some substances?
It changes their color.
Where may we find an example of this?
In trying to match the colors of thread or silk at night.
Why is the color different by lamp-light from what it is by daylight?