Many swimmers have trouble finding a swim cap that keeps their hair dry. The biggest reason that most people wear swim caps (other than to prevent ear infections) is to protect their hair. Because there are so many hairstyles in this world, it is easy to see why folks could be confused about this dilemma.
You can keep your head above water when you swim a slow breaststroke, but for all competitive strokes your head stays at least partially submerged. Brightly colored swim caps increase your visibility to boaters and jet skiers in open water situations.
Finally, be careful putting your cap on! Long nails or excessive force will put holes in even the strongest of swim caps, yielding them useless.