Two tennis players playing with each other wearing identical clothes is a tennis tradition with a long history. It’s annoying to tennis fans because sometimes they can’t tell the difference between the two players.
Sponsors such as Nike, Adidas, Fila, and others choose a clothing design for a tournament for a particular season (eg. clay court season or grass court season). Players sponsored by these brands wear these clothes and sometimes end up playing each other.
Only a few top stars such as Rafael Nadal and Roger Federer have been able to get unique clothing that no one else wears at the tournament.
Tennis sponsors can do better. At least when players find out they are going to play each other and are sponsored by the same company, the sponsor or the players can coordinate their apparel so they don’t look like twins on the court.