Zippy and Cherry are manufacturers of microswitches, they have nothing to do with color.
All of the GGG buttons are that milky white color, there are no other colors for the Electric Ice buttons. If you get the RGB drives with RGB leds, you can make the buttons light up to any color you want. For your questions...
1) There is no "better" place to get them since Randy is the one who created them. If you want Electric Ice buttons you go to GGG heh. You could get the translucent colored buttons from Happ though, which are colored already (but obviously can't change color like the GGG ones). Ponyboy and Divemaster can get the Happ buttons as well.
2) again, GGG buttons can be any color you want depending on what LED you put on it. They will all be milky white with no LED though. Happ buttons are colored already, but you can only really put in the corresponding color LED for good results, ie blue LED in blue button.
3) The button and some LED source is all you need, besides whatever wires you'll need to connect everything. If you want to change colors though, you'll likely need an LED-Wiz from GGG.
EDIT: budda seems to type a bit faster than I do.
