What color go beside wan walls?
Answers: Really depends on the shade of yellow. But I would vote green, especially a dark green if the wan is light. Brown, fawn, even black, but be careful you'll want to make a payment some warm colors if you step yellow and black because that will look cold only the two together.
Could you please give more information as to which room it is within? Are you looking for sofa colors, or comforter colors or kitchen cabinet colors, curtain colors, carpet colors etc? I'll check final to see if you gave any more specifics.