I think JayC hit the nail on the head.
I have a fish tank, very heavy planted with red cherries in it. It has been running for years and I am now at the stage that there are probably more brown wild type shrimps in there than reds but it would now be too big a job to start sorting it out so with hindsight I wish I had culled the poor quality from early on. I am not over bothered though as it is a general tank and I am more into the Taiwan bee shrimp now, and they don't have the same problem and are in a tank by themselves. I will fish out some of the brown ones to dump in the new betta tank I am setting up, but when I had a betta before he ignored them and they flourished in his tank, still I think they do good even if they can't really be seen easily.
You could sell on the lower quality ones either as food for people to use for big fish, or beginners shrimp? At least you only need 1 cull tank and can dump them all in together!
Simon