At one point or another (reptile trade industry) there have been "selective breeding" taking place to keep/enhance the traits (i.e color/patterns) of the reptile (not talking about hybrid).
So yes, there have been interbreeding of panthers, veils, etc chameleons. Naturally the gene pool gets smaller and problems do come up (after so many generations) so an occasional outside addition (introduction if an unrelated animal of same species) is key to keep targeted/ideal trait. This takes time and good record keeping.
As hobbyists, it's not worth going down this line as it's time and resource ($$$$) consuming with no return on investment. Leave that to the Pros that do it for a living and we simply just enjoy the beauty of the creatures that has been selectively breed for us
Or obtain another another of the same trait with unrelated bloodline and start your breeding project. I totally understand the urge that every hobbyists would have in wanting to breed these beautiful creatures, just do it with responsibly, and think it thru.....what are you going to do with all the babies Don't get me wrong, that's a great problem to have since you have been successful in breeding and incubating a clutch.