I was playing Portal yesterday and finally got to the end map. I turned on noclip and flew down to the hidden cake room (intended for a cutscene at the end of the game where the camera flies through an industrial-looking tunnel and ends up at the cake). After that, I went up to another hidden area outside the Aperture Science Testing Facility that was also for a cutscene where flaming pieces of GLaDOS fall from the sky. I've seen a lot of YouTube videos where people noclip outside and the asphalt in the parking lot was gray like it was supposed to be. When I noclipped outside, the asphalt was, to my surprise, purple! My guess is somehow the normal map showed through as well as the diffuse map. I've posted a screenshot of this glitch.
