blacksnake,
Candy colors are nothing more then a tinted clearcoat. When you apply, let's say a "blue" tinted clearcoat over a white base, you will get a bright blue. If you place the tinted blue clearcoat over a gold, you will get a nice rich looking blue. If you blace it over a black metallic, you will get a very deep blue metallic.
Different companies, including PPG, make candy apple type paints, but the most common and I feel the best is House of Kolors (Valspar)
You can even make you own if you wanted. You must use the "transparent tints" on the mixing machine. You can mix this with a basecoat clear. Even though you can make your own, you still won't get the exact same results as a paint like HOK Kandies.
Their candies are very "rich" looking. When placed over different basecoats, you will get different results.
Check with your local auto body supply store and ask them if you can check out their House of Kolor Kandy chart (most everythink that starts with a "c" will start with a "k" in the HOK lingo)