What’s the difference between yellow squash and zucchini. As far as cooking goes, not much — just their skin color. We substitute one for the other all the time.
Both are so-called summer squashes that are picked while still immature, so that their thin skins and soft seeds are still edible. A yellow squash is of course yellow, with either a straight body and smooth rind or a crookneck and bumpy skin (which looks odd but is perfectly fine to eat).