I see a red door and I want to paint it black:

The rating of copper bus bar and systems used in electrical equipment depends on many physical characteristics. An interesting fact is the colour of the bus bar. There is a tendency to tin plate bus bar, making it a shiny item. This actually decreases the ability of the bus bar to radiate heat. Many ratings are established for bare copper and as the copper ages its emissivity improves. In fact you can immediately gain that advantage by painting the bus bar black or applying a homogeneous black coating like epoxy. Improvement in emissivity may reach up to 15%. As is always the case. verification by test will stand the test of time.