One of the things I noticed when I first bought my BMW E46 was that the area behind the rear seats (the rear shelf) had a purplish color to it, which was very noticeable when I looked through the rear windshield. This is an extremely common issue on the E46 and is essentially caused from the fabric being constantly being exposed to sunlight. Over time, the rear shelf fabric will fade until it changes color from it’s original color of black to a lightened hue of purple.