Bacterial infections usually have a yellow edge to them . Fungal and leaf spot infections are usually brown. Your roots look as if they might have had a bit of breakage or damage, which causes them to brown. Their roots are white when dry and turn green with white spots when wet. New growing tips on healthy roots are usually brownish. Vandas like a lot of water and need frequent fertilizing as their roots are hanging out in air.This is a big Vanda Sanderiani.