Three-Color Design Principle
The 3 color rule is a guideline for choosing colors when designing websites. It states that for visual harmony, websites should contain no more than 3 main colors. This color palette typically consists of a dominant color, secondary color, and an accent color. This site suggests that the dominant color should cover about 60% of the visual space, the secondary color should cover about 30%, and an accent color covers the remaining 10%.
I read somewhere that each category can be a family of related tones rather than a single literal color. That’s what I’m going with, because stridently adhering to only three colors is too harsh.