There's more than one legitimate fish with the sulfur/sulphur head nickname, including what some call 'sulfur head (or crested) lithobates'. So 'sulfur head' is in the eye of the beholder as far as what fish it means, depends the circles you travel in, what the seller called the fish, etc., and it's relatively meaningless to the actual species name by which the fish should be identified. Sulfur head peacock is Maylandi according to anything I've seen. Similar looking Malawis aren't always easy to ID from a screen image. Color on the screen isn't always 100% accurate, color may vary with mood, egg spots may vary with individual, all of the above plus blaze may vary with specific location a particular strain originated from, or, depending where they were sold, there's the possibility of a fish with crossed genes in its lineage, etc. etc.
As far as OB peacocks crossed with other fish, it's happened to me a couple of times-- not by design. Technically, OB peacocks are already a hybrid and this plus the not uncommon Malawi cichlid willingness to spawn with whatever other Malawi is in the tank when mates of its own species aren't available, and occasionally even when they are... and there you are. From what I've seen fry will generally be a mix of OB individuals and individuals that are a less pure, less attractive version of whatever the other fish was.
For some years I bred several peacock species, bred some OBs for a while, and, based on what I saw on the occasions it happened, crossing OBs with other fish doesn't especially give you something you can't selectively breed from OB parents anyway. Since they're a man made strain in the first place it's not like you're corrupting a pure fish from the lake on the OB side of it, but on the other side, whatever species the other fish is, you get lower quality versions of a no longer pure species-- if all of that makes sense.
