That is the question! When I saw them I thought they were banded leaf monkeys (because I didn't know there was anything else in the forest). However, on reading @Chlidonias's recent thread I realised the one on the left is a dusky leaf monkey. On the right I am not sure now.
@FunkyGibbon
True. It does seem that the one on the left is clearly a Dusky leaf monkey, but the one on the right is more unclear. The sun is shining through the tail, which makes the tail look light grey. It might be grey or black - we will never know without close examination.