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).

Recipe: Zucchini Soup With Lime (Cookthink)
Recipe: Grilled Shrimp And Squash Kebabs (Cookthink)
Reference: Cucumber vs. zucchini (Cookthink)