Colors were decided quite early in the design process by a committee, and were chosen to be consistent between the CM and LM:
October 28, 1963. - An LM-CM displays and controls commonality meeting was held at MSC to explore areas in which commonality might be achieved and to provide a plan of action. Areas discussed included principles of layout, switch and nomenclature conventions, and common specifications -- both functional and environmental. [...] Signal lights, colors, and extinguishment techniques were agreed upon.
Apollo Experience Report: Crew Station Design and Development, NASA Tech Note D-8178
Since the Mercury program, astronauts have had the most say in the design of spacecraft cabins. (They are the ones who have to live and work there.) It's therefore likely that there were astronauts on this committee. As all of the astronauts were pilots, they would probably have picked the aircraft colors that they were used to. And the LM contractor (Grumman) likely already had those colors on hand and happily obliged.
Specific colors are as follows:
Even though the control panels and floor of the LM were made of aluminum, there were problems with stress corrosion, and thus they were painted. According to NASA Tech Note D-7290, p. 4, the control panels were painted in
These paint numbers are from Federal Standard 595, used from 1956 to 2017.
D-7290 also describes the colors of all switches, controls, indicators, and displays in its Table I. It is too lengthy to include here. Many of the colors are "aviation" colors such as
aviation yellow, etc.
The ceiling originally had exposed cabling. When astronauts raised concerns about damaging the cabling, a perforated glass-reinforced plastic ceiling cover was added, in its natural off-white color.
The handrails are their natural material color.