No, unless it is a truly odd situation i.e. someone painted them with oil paint, or exceptionally rusty one would not.

The normal finish for side plates and receivers is case hardening, colored, left french gray, or sometimes buffed to a silver finish. Sometimes they are blued, i.e. so called funeral guns, though often when found it is not original.

More information about the gun, make, model etc, current condition, and pictures would help.

Michael Dittamo
Topeka, KS