I think green is the best color for attracting the plankton that attracts the baitfish. All the more expensive commercial models are green. I have seen some build them with white and green. I ordered a roll of the green leds last week to make me one from instructions here on cdc. I don't think length is going to matter. More light equals more food for the baitfish which means more baitfish and hopefully more crappie. So bigger an brighter is better. I have seen them from 6 inches up to 3 foot or so.