"Yellow mustard" refers to a type of condiment that is commonly used on hot dogs, hamburgers, and sandwiches. It is yellow in color and has a tangy flavor. Full definition
Add to a pot with sugar, diced onion, grounded coriander seeds, two tablespoons of apple cider vinegar, one tablespoon of grounded yellow mustard seeds, salt and pepper. (greenevi.com)
I'm sure the recipe would work fine with yellow mustard seeds as well, just wont be as strong. (canned-time.com)