It doesn't really matter as long as you're using attacks for Pokemon that require colorless energy. For example, if you've got a fire type pokemon but it needs a colorless energy to use Scratch, just hook a water energy to it and you're good to go! Unfortunately, this is going to make your deck pretty weak. I'd suggest using a maximum of two or three types if you want your deck to have some degree of competitiveness. If you're making this deck just for the hell of it, and don't mind losing just about every game, there's nothing stopping you from adding at least one of every type.

Random, barely relevant story: For a while, I was so excited about drawing a particularly badass-looking Mewtwo ex (the old one) that I put him in my strongest, and most-used fire deck. Even though I couldn't use him, I liked to think that he gave me, and my team, a mental boost. It didn't really affect my game too much, it just gave the game some laughable situations! Best of luck to you in your Pokemon TCG endeavors.