The light from the exploding Rutan mothership leaves Leela temporarily blind and causes pigmentation dispersal. (TV: Horror of Fang Rock)
Pigmentation dispersal could cause the eye to change colour. When a Rutan mothership exploded over Fang Rock, Leela turned, against the Fourth Doctor's instructions, and saw the blast. The flash prompted pigmentation dispersal which changed the colour of her eyes from brown to blue and left her temporarily blind. (TV: Horror of Fang Rock)
