What is the difference between whole grain mustard and regular yellow mustard?
Is there any taste differences between whole grain mustard and regular yellow mustard?
Is the difference primarily in terms of texture and composition of each mustard?
Also, could each be used interchangeably?
"Regular" yellow mustard is actually colored; it's quite possible to have a plain, vinegary mustard without the yellow color too, even if it's not common in the US.
I think you should clarify where you live and/or what brands you have in mind, because the current answer (that from a US perspective, "Yellow mustard is usually very mild") is very much at odds with my experience of yellow mustard (English mustard, AFAIK the hottest type of mustard).
@Peter excellent point. I was assuming US mustard in my answer. In addition to English mustard, there is also Chinese yellow mustard.
The difference is that whole grain mustard tastes just AWESOME. Most yellow-colored mustard tastes like crap and can only become edible in the context of the umami mess of fast food. Not that I don't give myself in for a hot dog. Just saying. Either way taste both on their own and the whole grain one is clearly more taste and less vinegar.
Yes, there is (generally) a significant taste difference between whole grain mustard and regular yellow mustard. Texture plays a part of it, but it is secondary to the overall difference in flavor.
I say generally because there's a lot of variation in each, and some extremes of one type may approach some extremes of the other type in flavor.
Yellow mustard is usually very mild, and vinegar plays a very strong role in the flavor.
Whole grain mustard is usually stronger than yellow, and the vinegar flavor is much less pronounced, if not altogether absent.
In many situations, one type can usually be substituted for the other, although it is a matter of personal preference, and many people will argue that some uses of mustard are appropriate for one type, but not the other (for example, I would never use yellow mustard as a condiment for cheese and crackers, but I would use a whole grain mustard for some types of cheese).