Chris:
In my experience fishing frogs and selling frogs, you need to have at least one color with a pearl belly as you noted. After that, consider dark and light colors.
Most that fish effectively select bait colors based on them being darker or lighter so that there can be a decent contrast to the water and surroundings.
I seperate mine kinda like this: Light: Watermelon, White, Pearl White, etc. Dark: Black, Junebug, Green Pumpkin, etc...
In a frog, the fish apparently can see the profile on the water better if the bait is darker or lighter based on the amount of light we are seeing/getting. So if it is real dark out (IE first morning or night fishing), the theory is to use a dark bait.
With all that said, I have caught on white at night and black in full sun. You can also look around at what other companies are doing with their colors. Ribbit frogs come in a variety of colors.
Jim