Know that if they cannot be certain that a horse of a given breed or very carefully considered cross, would probably be something desired by those in that breed or cross, they don't breed. That usually means the sire and dam are registered or at the very least, their background is known and documented. The responsible breeder, knows that the sire and dam complimented each other and did not contain the same conformation faults. Even if they are sure they will keep the offspring for ever, they know that if things should change, there would be a ready market for the baby they produce. They know that even in the best considers breedings, the offspring doesn't always turn out as well as expect. They always geld colts before sale, of any horse who is questionable, as to breeding quality.
Often think it's fun to bring up a foal. They know nothing of the background of the horses they breed and couldn't tell you their faults, if asked. They breed often, because they have a mare and a handy stallion, who lives close by. They know nothing of the possible market for the foal, if they cannot keep it. Some even think they will make money, breeding and selling, iffy foals. Most are not true fanciers of their chosen breed. True fanciers, look to the future of the breed and know they are producing the best quality possible. Irresponsible breeders, whether the animals are registered or not, just breed and without knowing the first thing about quality or genetics etc. They don't care. They have done no homework, know little about their breed, know little about genetics and just think it would be fun to breed, to get another like their little 'Cindy' or whatever. And their little offspring, seldom turns out to be just like little Cindy.
Same in dogs. This is why we have six million dogs in the US, killed in our shelters each year. Horses or dogs, it's the sad fact, that our animals are being indiscriminately bred each year.
As to colour, on what you have already bred, you can go here, to get some ideas.
Horse Testing - Equine Genetic Testing
However, without knowing the true colours of the horses involved, it might not be realiable.