I only mentioned it as I understand that solids should be mated to solids & parti's to parti's. 
In general that is true. On very rare occasions a show breeder may cross breed colours with a very specific goal in mind, then return to the original colour (solid or parti) Since they have a breeding goal the puppies sold will usually have spay/neuter contract and/or limited registration.
When I wanted to breed my blue roan bitch to a black male, the stud dog owner grilled me very carefully on my reasons for wanting to do it, what would happen with the puppies, and what were my plans for the next generation or two. As well she should.
But in the case of the rescue dog that Joelf saw, I'm going to assume that it is from back yard breeding, someone just bred two cockers together.
As Nicola said, colour is a non-consideration in working dogs, so you are liable to see all sorts of colour and markings and all are correct.
There is nothing wrong per se with a mismarked dog. The markings have to do with the show standard, so a mismark only means it cannot be shown, the dog is not defective. The breed clubs have a certain vision of what the correct dog looks like, which probably means little to the average pet owner.
There is also no real way a parti can be mismarked, although from a show standpoint there can be markings that are less desirable; for example no mask at all, or a half mask with the white side on the "show side"
All cosmetic and not an issue for a pet
