>Attach Rainbow Energy to 1 of your Pokémon. While in play, Rainbow Energy counts as every type of basic Energy but provides only 1 Energy at a time. (doesn't count as a energy card when not in play.) When you attach this card from your hand to 1 of your Pokémon, it does 10 damage to that Pokémon.(don't apply Weakness and Resistance.)
There is nothing on the card that tells you to discard a Fire Energy, so no.