Truth be told, I haven't been able to find a single reference to official regulations regarding the appearance of HEIC drums. I looked at Boris Mollo's The Indian Army, John French's The British In India and the recent Osprey MAA on the armies of the East India company along with a couple of other books, and none bother to describe HEIC drums apart from a brief mention of brass drums in the Osprey book. I suppose no one will be able to fault you if you paint yours brass with coloured bands (in the second pic from the top, it's hard to tell whether the drum is full brass or if the bands at the top and bottom are yellow : I'd lean toward the former but I'm not sure).
If you really want expert advice on the question, drop Mike Snook a line via the Iron Duke FB page : if anyone knows for sure, that'll be him.