Yeah, I think I culled about 4 that were dark like that. It can happen in any line, You have to cull against too much color and too little color. I like to see broken up pattern over the backs and spots on the bill and legs. By cull I mean I sent them to pet homes to be pond ducks, I can't kill them. I just won't be using them in my breeding program because I consider them as faults..... since the color is to be broken up and not a solid color. 
I carefully select my breeders and only keep good pattern, spotted beaks and spotted legs etc......  I have a few chocolates, but would like to get some blue, silver, and lavender in my flock also.