I'm not familiar with chocolate genetics but that looks like red leakage. I don't think that is going away, and yes it is inheritable.
Leakage can mean different things to different people.
Bottom line though is that isn't going away and he carries genes that he shouldn't for a chocolate and it will be passed on to a percentage of his offspring.
I wouldn't use him unless you have no other options. It will be a lot of work and a lot of throw away chicks to get rid of it.
Sadly, I agree on all counts.