This looks like an officer of a line infantry regiment to me, grenadier company (see badge on cap). My first reaction on reading about a black uniform was that it could be the Rifle Brigade, whose green uniform was very dark that it could be mistaken for black, but the cap badge and other unifprm details rule this out.
Am not sure what the Osprey pictures are intended to show. Here, figures 1 and 3 are clearly wearing greatcoats over their uniforms, picture 2 of the bugler of the DLI is the one that should guide us for this figure.
I think, therefore, that Nap's original advice regarding a red tunic is correct. The trousers should be dark blue. The over-jacket looks like a piece of personal kit, possibly this officer had previously been in India and had bought it locally.