A whole generation of gamers grew up believing that gray is the only color for game cartridges thanks to Nintendo's choice of striking yet drab color pallete, but as GamesRadar points out, sometimes the gray's gotta go.  Nintendo had a knack for giving their game paks a little color when a special title burst forth into the world, but they're not the only ones that knew how to change the color of their plastic.  Sega got into the act as well, as did third-party publishers such as Electronic Arts.  Here's a piece of the article that fondly remembers a certain golden Nintendo Entertainment System title:

A dazzling gold Legend of Zelda immediately set it apart from every other game on the market, let alone the NES. When struck by sunlight it seemed to radiate energy like the Triforce itself, a feat that managed to make the lifeless plastic feel as integral to the Zelda experience as the groundbreaking gameplay.

Aside from special Zelda games (I preordered Ocarina of Time to be certain that I would own a golden game pak), I was always disappointed when I opened a box to find a non-gray cartridge inside.  That gray shade is just so iconic in my mind that paks such as the tiny yellow Donkey Kong Land just do not seem right, and don't even get me started on how much of an eyesore the massive banana-tinted Donkey Kong 64 looks next to my nine standard gray Nintendo 64 game paks.