Hair that is striking in its length, volume, or color makes a very dynamic visual, and as such, many a work of fiction will include characters who have it. But wait! For some reason or other, the person with the striking hair needs to be disguised so that either other characters, the audience, or both don't realize it's them.
The easiest way to do this is to conceal their hair under a helmet, a wig, or with a hat, cap, or scarf. This also gives the author the potential to toss out The Reveal with a dramatic explosion of flowing locks as the character's most prominent attribute positively identifies them for all to see.
