I have a blue merle, and she works, and so far she is really good at it! I think it is unfair to say that there aren't merles out there that are worth breeding, but I do think it is irresponsible to breed a BC just to get one attribute. They should be bred to maintain an intelligent, athletic, beautiful, working breed. So, I Might be a little partial but I hope my next one is another working merle. I know it might take longer to find one from a reputable breeder, but I don't think this means I am looking for a fashion color, some people are just drawn to certain colors more. Second best I like dogs that are mostly black, I think different people like different things, and as long as they are bred reputable, and the owner is responsible I don't think color matters either way.
I think that the dogs should be bred to work, because when you start breeding for other qualities you lose some of the original attributes that make these dogs so great. I think it is amazing that they excel at so many activities, but the reason they do is because they are herding dogs. But, I think a lot of times people get caught up in the sport, and there animal becomes a tool, and at that point people will breed whomever to whomever to try and get some advantage. Which in my opinion these people aren't worried about preserving working heritage but getting themselves the best sport dog. Sorry if that was offensive to anyone, I didn't mean it like that towards anyone on this board.