Many thanks for the answers, chaps

Sepoy1857 : yes, I was familiar with the info French provides in his chapter on the mutiny. But since his list post-dates the first Anglo-Sikh war by twelve years, I wasn't too sure what to make of it. As to whether the rifle company replaced the light coy or not, French remains guarded, which suggests that there's no solid evidence one way or the other (he writes that they "
seem to have been an addition and not a replacement" - my emphasis on 'seem').
In the end, I think I'll paint a rifle company for the 42nd BNI (which was after all a light infantry regiment, at least on paper), and possibly for the 48th and the 26th as well. As Gluteus says, it is most unlikely anyone will produce period colour photographs to prove me wrong anyway