I go by the "contrast" theory ..... two colors on the bait; one dark, one light. This gives the angler a visible color in most all water conditions. Also of note, is the fact that fish can see better in dark water than humans can, so the "dark color/dark water - light color/clear water" theory may not be all that important.
It may also be important to note that fish can see much better, farther, and with more clarity in cold water.

I don't fish muddy waters, and rarely have to fish "dirty" waters. Most of the lakes I fish are usually lightly stained & have a foot or two of surface visibility (before a chartreuse jig disappears from sight). In most of those waters I tend to use purple/char, blue/char, solid chartreuse, or solid pink as my primary choices for colors or color combos. The combo colors are usually plastics, and the solid colors are usually Road Runners.

Clarification : when I say "purple" or "blue" in combination with chartreuse, talking about the plastics I put on a jighead, they can run the gambit of variations of those colors. Blues or purples can be very light to very dark versions of what the general idea of those colors are. And I include colors like "junebug" in my "blues" category.