I believe, you mean what two colors make yellow?
Well, none really, because yellow is a primary color.
A primary color is a standard color, the primary colors are: red, blue, and yellow.
Every color in the universe would start as a primary color, such as: blue and yellow make green or blue and red make purple.
No two colors can be mixed to make a primary color, it just doesn't work.
So, frankly, the answer to your question is none.
red and orange
Mustard is a dark yellow color. You can make it by adding a little gray to a lot of yellow. Instead of gray, you may want to add a bit of brown.
What makes mustard a "pub mustard" is the fact that honey and possibly Irish whiskey is added to wholegrain mustard. Pub mustard can be used on sandwiches and can also be used in dips.
Yellow & brown.
Mustard is a hard color to match with but i found a couple of choices:lime greenredaubergineemerald greenwhitepeach pinkHope this works out for you!!
Wisconsin Spice, Inc. makes mustard in Berlin, Wisconsin.Middleton, Wisconsin has a national mustard museum with 5,676 types of mustard.http://mustardmuseum.com/the-mustard-museum/
brown
yellow and cream
white
Mustard stains because it is a dye stain ,which makes it difficult to get out.
Yellow and blue.
yellow & red
Dry mustard is usually used with other spices, has a slight mustard taste and makes the food yellow.