>>8717583This is a good example I think, basically there is a layer of a different color paint under the main coat, usually just around edges. You can make subtle changes to the color of your main color. Think of it like the difference between primer colors, white for bright vivid colors, grey for subtle, black for metallic and dark, ect.
I personally don't really care much for shading, i prefer my kits to look clean with small details picked out with panel lines.