Sorry , it looks more like the image processor is failing. I don't believe the color wheel can cause what you're seeing, especially since you say it's fine when first turned on and the lamp DEFINITELY cannot do that.
One other possibility, Did you check the color wheel sensor. On a HD20 I would see something like this when it needed cleaning. Never saw much for dirt but a good dusting of the sensor with a small soft brush and clean air would solve it for months of watching.