Seven wonders building a stage
You can use any resources, including those from yellow cards.

Paying for a Wonder stage is pretty much the same as paying for a structure on a card. The only difference between resources produced by yellow cards vs those produced by brown and gray cards are that yellow card resources cannot be bought by neighboring players.

From the rules:


  The resources of a city are produced by its Wonder board, its brown cards,
  its gray cards, and some yellow cards.
  To build a structure, a player’s city must produce the resources indicated
  on its card.