If you like it hot, use it right away and store the remainder in your refrigerator to slow down the loss of pungency. If you like milder mustards, allow the mustard to age at room temperature. It's the turmeric, not the seeds, which make it yellow. Dijon is spicier and sharper in flavor and can range from mild to hot. Usually it's made from brown seeds, white wine, unfermented grape juice and seasonings.
English mustard is very hot and intensely yellow.
It can be smooth or coarse and soft yellow or brown. Chinese mustard is very hot and used for dipping. Prepared mustard can be stored for two years - keep it in the refrigerator after you've opened it. It's easy to add more intrigue to prepared mustards. A dash of green peppercorn and mustard will perk up your beef dishes.