First of all, the funnels pours out more smoke than in SS08. Second, the colors of the ship seem darker than in SS06. And third, well...that's all I can think of at the moment.
But, the smoke may not have been as dark once the boilers started functioning, a bit like a solid fuel burner, on the start of burning, smoke comes out, but then, once its settled, less smoke is produced. The wood on the decks is a lot more accurate on the SS08 version (from what I understand) as the SS06 decks are very bright.
Thats my opinion anyway, someone who knows more about this should comment on this one, as I'm not 100% sure.
Jack.