It is much easier with a stripy livery, blue and grey, something and cream etc.. as you can get away with just suggesting the vertical elements of the frame, and leave it to the viewer to imagine the horizontal bits which tend to be bordered by the livery edges anyway. Interestingly, on the SVR you see Crimson and Cream carriages with different 'depths' of cream stripe depending on whether the frames are there or not.
Anyhow, getting a bit off piste Ropley wise...!
I reckon that, though it is a more involved process with the plain green, it might yet be worth a go?