I know that in Australia a buckskin or brown based buckskin Welsh will be registered as "dun" despite the fact that the term is incorrect. I don't know about Connemaras though. He is DEFINITELY roan, and there are clear markers of cream (the gold in his face). I think you're very unlikely to have dun in there but the only way to be absolutely certain is to test. Unlike with roan and cream in this case, he definitely has those.
Chiilaa you're the one who spotted Satin's splashed white. Considering how minimally expressed she is (blaze and a sock and no other white, just to remind you) I'm impressed.
I'm not saying Chiillaa is wrong, in fact that has got to be the closest description of his colour i've ever come across, But being the UK we are somewhat behind with our colours and if I told someone who asked what colour he is 'brown based buckskin roan' I would either be laughed at or told there was no such colour, To answer Chiillaa's question no he doesn't have a dorsel stripe which is why I have always questioned his Dunness and I also thought that Connemara's could not be Dun as they are not recognised n the breed standard? Could he possibly be Gruallo? (sp)