I had one dark female delivering about 3 or 4 Blondies with each batch of fry, so I seperated the blondies every time and now have a tank full of blondies who seldom throws back any dark fry, and if they do, I remove those before they are adults.
As for the colour.... on the left are a few males and at the right side of this picture are 2 females. (notice also the small fry swimming around with the parents)