Thank you for all the helpful suggestions! I ended up getting some boxes of color catchers, and tested a corner of the fabric in cold water and didn't notice any bleeding so I crossed my fingers and toes and put it in a cold wash with 3 color catcher sheets. Thankfully, no bleeding at all, didn't even see anything on the sheets. I'm sure it also helped that the color that was appearing to be an issue was a lighter yellow.
I see lots of people talk about washing in warm or hot water - what is the benefit of that vs. cold? I guess I've just always washed everything in cold (except socks, underwear, or bedding with special instructions). I'm too lazy to separate laundry so this has always insured no color bleeding. I carried this practice over to my fabrics.