The traditional chef's hat or a "toque blanches" was developed in 16th century France as a means of symbolising your status in the kitchen with chef's hats being the highest. The pleats in the hat were also a way of showing how experienced a chef was. Traditionally, the toques had a hundred pleats for senior chefs, some still have a hundred but it has become less common in modern kitchens. They are generally white as it is supposed to denote cleanliness and hygiene.
Interestingly, the hundred pleats are representative of the hundred ways a chef can cook an egg.