French Napoleonic line
pontonniers were attached to the corps of artillery and wore the dark blue artillery uniform shown below :

The mounted figures are
conducteurs du train whose job was to drive horse teams : they belonged to a separate corps and therefore had a different uniform of sky blue faced brown. Here's one of them on the right :
However, the figures you have circled are an Imperial Guard engineer officer and an ADC. The officer is wearing a undress
surtout and should look like the figure on the right below :
Re the ADC, use the plate below for reference - sorry, the pic is rather small and I don't have anything larger but the colours can be easily made out. I'd use the figure on the left with the nice red hussar breeches :
The pontoons themselves appear to have been mostly painted artillery green, though I've sometimes seen illustrators depict them in natural wood. I'd go for artillery green myself.

The planks and beams would obviously left in their natural wood colour.
Hope this helps