I think only silver or chrome finish work properly with candy.
I tried a black base coat once and that didn't work at all. White just made it look like the colour on top was pale. Gold made everything look brown and yellow was pretty much the same.
The difference between a silver and chrome base coat is the silver gives the final finish a slight shimmer like a pearl finish and it isn't quite as reflective as the chrome.
The first few coats of candy you put on you'll think it's never going to be rich or dark enough. It's very subtle for the first few but it starts to pop after about 5 or 6 then it gets darker and darker as you go. The purple I did was almost black when I finished but it brightened up a lot after sanding and buffing. Once it's finished the more light you put on it the brighter it is.