There is a huge difference.
Your example is not the difference, though.
Rainbow Energy cards count as all types of energy cards while in play.
Since they always provide all colors, if an effect is looking for a specific kind of energy card, it will see a Rainbow Energy card that is attached to a Pokemon.
You would take 30 damage in your example.
Now, if it had said "basic Energy card", then it wouldn't see the Rainbow, since it is a Special Energy card.
There are other times where effects make a difference beween energy and energy card. You would see those differences with something like Double Rainbow Energy or Boost Energy.