When I saw the title I obviously thought it was going to be about 4 color theorem, so I was disappointed but then I considered... Is there actually a 4 color t

When I saw the title I obviously thought it was going to be about 4 color theorem, so I was disappointed but then I considered... Is there actually a 4 color theorem like rule for text and background colors needed, probably there is a design rule but that isn't a mathematical rule the way the 4 color theorem is. And I guess that the rule is just text and background each need a color - so two colors.