Adding genes had never made a difference in mutations that have known issued.
The majority of people that want to work with similar colors have switched to Ultramel because of the fertility and defect issues in caramel, now even if you were lucky enough to produce some perfect animals, and some do ask yourself this
Is it worth the risk to produce some deformed animals?
Is there a market for the perfect animals that would be produced knowing that most people have abandoned the project long ago?
Personally when I breed I know that there is always a risk and not every animal will hatched out or even hatch out perfectly however I chose not to try to produce animals that have higher/known chances of producing animal with physical deformities.
I believe that it is a dead project and that the caramel market will never be where it onced used to be.
I am sure when you ask yourself those question you will find the right answer when it comes to your future projects.