Black and white are the hardest colors to get. The fruits change the RGB values of the feathers by varying amounts, but if anything over or underflows then it messes with the end result. And what you read about crossing plants is somewhat true. A lot of seeds do only come from crosses. These seeds just happen to come from a fairly cheap and ready source. Gardening is probly a more involved system then it needs to be considering how little it is needed in the game.