Thomas, Edward, Henry, Percy, Gordon, and James all received their numbers in 1951, when Henry the Green Engine was released. Prior to that, it's implied they would have had numbers, but they're never revealed to us (as far as I know). Toby would have carried the number ranging in the 130s in GER days and 71-- in LNER days. The date he was built determines what the blank numbers would be. Duck and Oliver carried their G.W.R numbers; 5741 and 1436 respectively. Donald and Douglas would have carried their numbers from BR; 57646 and 57647, again respectively. Daisy seems to have arrived with no number and was numbered D1 on Sodor. BoCo arrived with D5702 as is BR number before being renumbered D2. As for Thomas' livery when arriving on the Island, it probably would have been in LBSCR Black with what I would say yellow letting on his side tanks like this.
Hope this helps!
Hope this helps!