If you are pulling together a design, say for an app or a web page, and you are relatively inexperienced at working with color, spend a few minutes reading this post. It’s short, and offers some simple techniques to help you make some relatively safe choices.
A strategy for picking colors for your design
The designer’s book covers are good. Seems to me he’s setting up a lot of cautious restrictions for himself for color. He’s also perhaps thinking of his vector work as “a work of art” instead of an illustration component of a larger design.