Hi guys,
I have it on very good authority, that the overhead panels of the B737 were coloured the two different shades of grey, to suit a special purpose, originating back in the -200 series, and just hasn't been changed.
The reason was during the initial certification of the -200, it was the first of the Boeings jets to operate with a two man crew, so the company had to prove to the FAA that they could handle all the various normal/emergency functions without a Flight Engineer.
But, during those verification flights, the aircraft was required to carry a Flight Engineer, and he was trained to take care of certain basic aircraft systems, should it be necessary!!
Those panels he was required to use were painted a different shade of grey to avoid confusion.
Well, I understand they managed to convince the FAA that the two man crew could monitor and operate all the necessary controls, though there are numerous incidents since then, indicating that, at least some pilots, cannot.
'believe that !!!
Cheers