D.M.
Presoaking in liquid tide and Biz will often remove yellow stains. Like many said... DO NOT DRY IN DRYER until you are satisfied that the stains are as gone as they will get. Heat from the dryer sets many stains. Hot water can also set some stains.
Another tip: Hydrogen peroxide and ammonia will often pull yellow stains from cotton tees (and other items). I have never had it pull color but it could. It works great on formula stains too. I just splash a little of each on the spots of a dampened garment and roll it up. Later in the day I will wash it. Repeat if necessary. Sometimes I just reapply without washing it through the day or overnight. I learned this when I managed a drycleaners, I saved many a tablecloth for my customers.