roots dont like light, so keep it out of the pot`s, paint em or cover em in tape or a bag or similar (tho remember to keep some good drain holes, roots don't like to stand in a wet grow medium all the time)
Yeah roots are very sensitive to the light, that's why lots of growers transplant in the dark so they don't add any stress to the roots. Black pots work best but any color is fine as long as the light doesn't leak through. I would advice against using anything white or clear though.
if it was a thick enough in white so if you put it up to the sun and can not see light trying to show threw it you be ok it would help refleced the light but better to paint a black one because light kills roots
i use white for my basil plants since .. well im evil Nah i just havnt got around to setting them up properly, But Yeah If to much light gets to the roots they will start getting all slimy and can rot. So be warned , have your roots in the dark