You can only have one and not the other. It is permanent.
I'm not overly bothered about either, my teeth are neither perfectly straight or perfectly white they are straight enough that i never needed braces or anything and they are certainly not yellow and dirty. Perfectly straight and white teeth look stupidly superficial and fake to me, but i suppose straight teeth actually have benefits while white teeth don't so ill go for that
I don't care how they look but straight is more practicable. Uncorrected teeth can be crooked which creates gaps and little spaces where food can lodge which is inconvenient.