I have read threads about this type of convict coloration. From my experience, ALL my black convicts with this type of coloration tends to only occur at a young age. Maybe fry-2inches or so. They will loose the black spots when they get older. Some people have theorized that its due to stress, some say its crossed with marble gene, and some have said its a hybrid. I dont think there is a real real answer because most all black convicts in the mainstream market these days are not as pure or as real as they used to be in the wild.
Marbled convicts are pink convicts that have black spots. Some marbles tend to change their marbling as they age.
I have a honduran red point male that has black spots on it too.
The one you have is not a marbled convict IMO, but a regular black convict.