Inside the shed the brickwork has been given a quick wash over with Humbrol 147. Thinned a little bit and swashed around with abandon, I think it looks reasonably close to whitewash which has seen better days and is wearing off the brick surfaces.
Since the shed has plenty of ventilation I've resisted the urge to paint the inside black. Locos wouldn't be in anything other than light steam when going in and out of the building so if there was anything coming out of the chimney it wouldn't have very much soot in it. For the same reason there isn't an enormous blast pattern over the door top - you only get these when the engine is working.
Using my pencil crayon method of colouring the brickwork went well. The faces aren't as pronounced as those on the Slaters version but they still picked up the colour OK. Special efforts had to be made on the angled ares above the stepped out bits at the bottom (can someone enlighten me to the correct technical phrase ?) but a sharpened pencil seemed to do the trick.