Smart people are awesome. More than that, they're astounding. When you see a genius's mind at work, it seems almost impossible. They know more than you; they can figure out things that confound you; they can see connections that you have never realized were there all along. In that regard, the genius very easily looks like the master of all knowledge.
In reality, a genius is usually good at one field. It could be sound or physics or flavor or color. In reality, though, the things that a genius knows about color really don't have any bearing on sound. So, if you have somebody who understands colors at a genius level, she could coordinate outfits, decorate homes, critique visual arts, help you with the presentation of meals. However, her set of skills would never encompass keeping a musical instrument in tune, or setting up the PA system at a stadium, or teaching somebody how to sing in tune.
In stories, though, geniuses are equally genius at everything. It's a common misconception, and an easy one to make, but by showing where a genius is weak, as well as where they are strong, you will present a far more believable character.