Now to add depth, to the discussion, I don't pretend to be a chicken breeder, I am just trying to keep the ones I have like they were when I got them. I have done a bit of farming with various other livestock, and I have dabbled with hunting dogs. Hounds would be easier for me to use to illustrate, because I am more familiar with them. A lot of people get the notion that if they cross a bulldog, for pure toughness, with a bloodhound, for nose, with a German Shepherd, for smarts, with a Greyhound for speed, that they would have a hound far better than the ones that people have been perfecting for hundreds of years to have those traits balanced within one family. Now, you might end up with a really outstanding individual, but it is much more likely that you will end up with a dog that is as slow as a bloodhound, the speed of the bulldog, the scenting ability of the greyhound with below average smarts that looks like a German Shepherd. Some of the traits are actually antagonistic to each other in some cases, dogs that stay barking up a tree good sometimes aren't as good at making something decide to climb a tree, sometimes dogs with a real good nose aren't very fast. This could carry over into fowl, in that high egg production might be antagonistic to efficient meat production. Crossing a leghorn with a cornish might not be a viable solution.
Getting the traits that you want balanced is much further compounded when we add silly human contrivances as phenotypic color selection. The best dogs I have hunted with have been bred by breeders who didn't give a rip what color they were as long as they got the job done. Breeding for balanced performance AND the right color add much more need for depth in the breeding program. Most unique color schemes most likely came about because a breeder noticed that the stock in his or her program that exhibited the performance or production traits they wanted also happened to come a certain color. It made for an easy marker for the ones that were bred right. It is much more likely that someone bred a breed that did what they wanted and the end result happened to be a certain color, than that someone started with a certain color and then selected for the desired production traits, in most instances.