Most likely they will just turn out to be low grade zz but I guess it depends on the type of flowerhorn you breed it with. You might get some faders but most will probably just look like washed out flowerhorns. A good example would be super g's (banned user) "rainbow flowerhorn."
oh damn... good to know then, I was thinking of trying this as well, was hoping to get some kok gene from a red devil I got recently... pretty much just for that reason.
There is a lot of good uses for hybridizing red devil and midas to make flowerhorn but you have to breed them with the right kind of fish and it might take a few generations of breeding before you get anything desirable. A good example would be red devil X vieja synspilum will make a rose queen flowerhorn. Some people have used red devils to create red texas also but it takes a few generations.
heres my rainbow i got its mom is a low low grade fh (trimac) dad is a midas or jk not sure but it has red eyes but here are the pics after fading read the thread above youll see the changes.