sincerely as find vintage color photos is impossible because the only color photos of the time they were painted thus unreliable for colors reliability and find photos in stored clothing colors used only in 1916 from so 'few soldiers, since we are talking of the first tank drivers in absolute of history, it seems to me very difficult, unfortunately, I'll want to go a bit 'to guess,we all know the denim pale blue color,should not be difficult to redo
I imagine that those suits were taken directly from mechanics and engineers and not produced on purpose so maybe using that as your search criteria you can find something.