In the end, it all depends on the color pallet of your game.
As far as specific color designs, you might ask the Graphic Design Stack Exchange.
From a UX perspective, you want to make sure your colors are accessible to all your players, or at least provide an option to alter the colors to cater to excluded players (for example, people who are color-blind). Having lots of different colors can make it more difficult to achieve a color accessible interface, depending on the colors you want to add.
The game's UI can also reinforce a sense of atmosphere you are trying to achieve in your game. Be sure to consider the context of its' use, and the feeling you are trying to evoke from the player. Having lots of different colors may make it difficult to achieve this atmosphere reinforcement if your color selection doesn't follow the color pallet of the game.