It's true.
Especially for the latin style dances, the norm is that eveyrone uses fake tanning products to really darken their skin before competitions. It's not quite as common for the more traditional waltz/foxtrot events at competitions, but happens there too. Personally I think it's silly, but I can understand why it happens in a situation where people have tens of thousands of dollars of training, several thousand dollar dresses, and perhaps a few hundred on personal grooming right befoe an event.
Of course ballroom can also be danced, and even competed, without any of these aspects, or with only low cost home-grown imitations of them.