Beginner: cell faces of surface cells
 

Hello, with my first example (tube) for coupling Star-CD with PERMASS via MpCCI:

how do i get cell faces of outer region via some coding? i dont want to do it with cursor select (cell by cell!). With LAYER command i have the cells on surface and i want to color each face of the cell differently so that face pointing outside is the shell/baffle which is the interface to PERMASS. I beg your pardon if my sentences are incorrect. Greetings