Why does a yellow flower appear yellow?
why does a black notebook appear black?

Filters will make colors look the way they do. a thing or an object will look white when it will be soon reflected this will cause all wavelengths to see that color. and black when it absorbs all wavelengths. Red, green and blue are the additive primary colors of the colorspectrum.

Exothermic,  physical change after it is already baked