I have heard about there being 50 shades of grey/gray.
No one knows the shade/shades used on 216 and early 235s; and, the shade/shades used on later 235s.
My belief (not confirm-able and not refutable) is that the darker blue-gray was more commonly used on low-pressure engines and the lighter (Ford-like) gray was more commonly used on the later high-pressure engines (except the green shown for some years' high-pressure Trademaster 235s at the link I posted above).
No one has proof regarding the shades of grey/gray.
