I know everyone is going to say you need a red light, and that should be your primary light. But I think its important to also have a white light and one other color (typically green).
The reason is simply that red light makes everything look red, and makes it hard to distinguish colors! Can you actually verify that the AVgas is light blue when you look at it under a red light? Can you see bright red, important items on a checklist? Reading red-text against a white background can be very difficult with a red light. On a VFR map, airport symbols are blue or magenta to indicate towered/untowered airports, but they both look the same under a red light.
So while your primary light should probably be red, you'll need alternate colors and plain-old white for many things.