The interior paint code should be the same as the exterior. If the outside has a different color than the outside you may be in trouble. With my experience finding paint codes with my customers this usually means the out side was painted in the past and the inside was never jammed and repainted. I know most GM's will have a code starting with a "U" followed by another code starting with a "U". This means the car is a two tone, but usually meaning a two tone exterior. Not sure if that helps at all.