First, I have no idea what kind of gym you'd be able to wear those Charlie's runner shorts.
Second, my advice is to avoid "double" colors. Don't wear a dark blue shirt with dark blue shorts. Or gray with gray (a.k.a. a "groufit") And never wear double orange.
Third, while 100% cotton is most comfortable, I wear non-cotton shirts because the cotton tends to get stretched out and get in the way of movement.
Fourth, go to a sporting goods store and look at what the mannequins are wearing.
Fifth, ask a woman with fashion sense who is into fitness.
Sixth, Nike makes the most comfortable fabrics. Under Armour is by far the least comfortable--it's itchy all over all the time.