There is no such thing as an "acceptable proxy".
The Head Judge can designate a proxy for a card during a tournament if and only if a card had gotten damaged during a tournament that can not easily be replaced. They can choose whatever they want, but they would of course choose something that promotes clarity.
A Basic Energy card does not fit that definition.
It would be easy to replace it with a real card.
You don't get to "bling out" your deck with cards that are "similar" to legal cards.