Yes that's mustard on my apple. Mustard is one of the condiments I am allowed on the HCG diet and I was curious. I would like to state this categorically with no equivocation: yellow mustard on apples is delicious. It's also visually appealing in this case drawing comment from my coworkers. And I'm going to put this out there, its really helpful when co-workers, who don't know what you are up to, come up and tell you how beautiful your lunch is. I've been making an effort to make my food visually appealing because like most people I eat with my eyes.