In general we do not vacuum metallize onto metal surfaces. There are several reasons, the main issues being: 1) Any oils or other contamination on the metal substrate will spoil the evaporated metal by chemically reacting with the metal, usually turning the metal black or brown, and 2) The evaporated metal surface will usually be no more reflective than the underlying metal substrate because of surface scratches/blemishes in the underlying metal substrate. The evaporated metal coating is less than one micron thick, so the coating precisely follows the microstructure of the substrate surface. The plastics we normally coat onto have mirror-quality surface finish (far smoother than 1 micron deviation) and this produces the highly reflective appearance most people are seeking. The people who chrome plate metals usually put down metal layers much thicker (several microns thicker than the surface deviations) or find other ways to “level” the surface – perhaps with coatings or other fillers that fill in the fine scratches.
Regarding gold color, usually this is not done with metallic gold due to cost considerations. Generally “gold metallizing” is done by applying a yellow top coating over aluminum or by using yellow plastic and metallizing on the back side of the yellow plastic. Sometimes people lay down various metallic alloys to produce colors such as “gold tone”.
In the case of a metallic aluminum part, you may be able to obtain a “gold” color by the use of appropriate anodizing techniques. Anodizing is the process of creating an aluminum oxide layer over the base aluminum and intentionally incorporating specific “impurities” to add color. Unfortunately Replex cannot help with anodizing.