Well, this is the one area that I can actually supply some expertise. My job with the US Navy deals directly with nuclear reactors. The reactor vessel itself can be painted a stainless steel, the large piping (coolant loops) associated with reactor is a glossy white, the smaller piping is an aluminum color, the steam generators are white uppers with steel lower sections, the pressurizer is the same, the main coolant pumps are stainless, the ladders and decking are stainless, the inner hull, structural support and bulkheads are white. Individual valves are stainlees steel.