Aw yaaas, shadows. Our eyes are designed to detect shadows, which creates some cool illusions.

Sometimes our ability to see shadows and the contrast around an object can cause us to misinterpret to color of an object, like this
So for white/black, those aren't colors, but they can be. Black is yellow and white is blue. So when shading or coloring white or black, you can use the corresponding blue or yellow. to create the shadows and even the base color. This is why a blue/black dress can look white/gold depending on the lighting around it. This excludes reflected light and color, which doesn't follow the same rules. If you were to paint a snow clump in the sunshine, the shadows are darker and blue, the base is an unsaturated light blue, and the reflected sunlight is yellow against off-white.
Fun fact, when you do some kewl drugs, your eyes start to see shadows as colors, because they are colors. But your eyes recognize them as different colors, not shadows on an object, which can cause a shadow to sometimes look like an object as your acid brain tries to figure out what you're looking at because you eyes have lost the ability to focus on moving objects. This is also why shadows can appear to 'move' on an object, like a still curtain. If you don't do drugs, some simple sleep deprivation can cause the same effect.
