The effect is not white just because it has an escape clause.

The design principle behind the escape clause also is iffy. I'd rather have "Destroy target creature unless its controller sacrifices a Treasure." which at least would advance the game state.

It really sucks that this becomes a dead card if an opponent just happens to sit on a Treasure they have no opportunity of spending.

I also think the grammatically correct form may be "Overcost Taxes" though "cost" itself is not quite the right phrase.