Here’s an example of the changing color of the walls from the Blu-ray (uncorrected). This sequence has some horrible color smearing that seems to be on every version of the film from 77 onward, but it’s also clear evidence of the wall sections being painted different colors:
The wall on the left has about ten points more green than the one directly beside it, and neither are gray according to the blu-ray.
JEDIT: Yes, Mike has also said that the walls were painted different colors - see his discussion about the wall sections abutting the droid alcove across from the Falcon, which was intended as a more neutral gray.