Temp, your rug is cotton and jute with a latex backing. The yellowish color is likely due to lignen found in raw cottons and color loss. Bleach would not be a good idea on cotton, but at $30, what do you have to lose?
Cyrnel has a good starting point. Hose the rug down, especially rinsing out your spotting treatment and let it dry to see what you have left.
Two cents worth from the resident rug sucker.
