Colorless Pokemon aren't very popular in the "today" decks. They're very seldom the life of a deck. Some common Pokemon are Kangaskhan, Chansey, and maybe Wigglytuff. But other than that they don't have much purpose.
What I'm trying to say here is that Colorless Pokemon don't rely on hard hitting abilities. They focus mainly on doing flat out, simple damage. For instance, When you see four colorless energy on a Colorless Pokemon, most of the time it will just do 40 damage. And if it doesn't it will have some other ability. Not a very special one mind you. Colorless Pokemon are simple and don't bother you with paragraphs explaining how this attack will work. They almost always are straight to the point and don't Confuse you with long named attacks.
Colorless Pokemon can be added in any deck. No matter how strategic it may be. There isn't a single colorless Pokemon that use non-colorless energy. But there are very few non-colorless Pokemon that use only colorless energy.
What I've just told is that Colorless Pokemon rely on very simple and easy damage attacks. But what about the colorless Pokemon that are stage 1 and even stage 2. Is there anything special for those kind of Colorless Pokemon. Yes, there is. Stage 1 Pokemon aren't everywhere. And stage 2 Pokemon are extremely rare. But have you ever noticed that they use coin flipping attacks much more often than their pre evolved forms. It may not be a very huge and important tech, but it can be useful.
Let's look over this
=Colorless Pokemon use very simple attacks
=The higher the evolution, the more coin flipping you'll be doing.
=Colorless Pokemon can go in any deck of any kind of any era.
There you go