Often erroneously translated as “yellow beans” or sometimes “yellow split peas” in some Thai cookbooks, thua thong (literally “golden beans”) is nothing but mung beans that have been hulled. They are used in Thai cuisine primarily to make desserts, although some savory recipes call for them.
Both unhulled and hulled mung beans are used in Thai cooking, but in most — if not all — cases, they are not interchangeable. When a recipe calls for one, the other cannot be used. And since the process of hulling mung beans is too tedious and complicated to do at home, it’s best to buy mung beans that have already been machine-hulled.