Switch was originally intended to be different genders in and out of the Matrix (hence the name Switch). It's possible that the white outfit was designed to highlight that her RSI was different than the others, as well as subconsciously project the duality of her/his nature with the black/white symbolism.

Why was Switch the only one wearing white?

The reason why Switch is wearing all white instead of the usual black is that it projects the duality of her nature originally planned in The Matrix. In fact, the detail hidden in the film's symbolism (like the red and blue pill) shows that the Wachowskis had a lot more in mind for Switch.

Who wears white in the Matrix?

Plus, when the crew makes their way into the Matrix post-Neo's rebirth, Switch wears a different color from everyone else. Neo, Trinity, Morpheus, Cypher, and others all wear black in the Matrix but Switch is noticeably wearing all white.