If you watch a horse race, you might see that some of the horses have brightly colored bridles rather than the more normal brown and black.
Most racing bridles are nylon because it's lighter than leather and every little bit of weight matters in a race. Because nylon bridles can come in all kinds of colors, there's now a growing tradition of using a bridle colored to match or complement the owner's silks.
The tradition is now spreading beyond racing and sometimes you might see a saddle horse with brightly colored tack, especially if it's a child's pony.
Some people, however, are averse to nylon tack because it's less likely than leather to break in an emergency.