My boyfriend wasn't looking at the store and picked up a "Butter yellow" cake mix instead of "Golden Yellow." Do we have to make it with butter or can we just leave it out and just use oil instead? Or do we have to go buy the right cake mix. We don't want to be left with a box of cake we won't use
For a boxed cake either type of cooking fat should render a similar result. The final flavor will be a little different, but it shouldn't make a huge difference and probably won't be much different than a mix that calls for oil in the first place.
If you wanted to keep the flavor similar while avoiding dairy you could try using butter flavored shortening instead of oil.