What color sheets are adults supposed to have?

I need new sheets for my bed. I bought white sheets at the beginning of the summer and despite me washing them regularly, the already look dingy. I went with white originally because I thought they would be easy to bleach, and while the bleach gets them clean, it doesn't make them bright white. Are darker colors betters? Do they show . . .ahem . . stains more? Did I just buy crappy white sheets (they're from target) and that's why they got dingy so fast? Help me be a real person please!