I've lurked around on this forum here and there over the last 2.5 years and 3040 Lamp hours since i bought my HD20, but my recent situation made me want to post as the info might help any others who were looking for the same info i was looking for previously, and i know this has been posted before but there have been conflicting posts from other owners so i thought it might show that the this has helped me out.
Recently, i started getting the colour changing/flickering issue after periods of around an hours usage, which slowly reduced to 15/20mins use, and then to 3mins use unless i used High Altitude setting.
I thought i'd bite the bullet and open my baby up for cleaning, and as others had suggested i cleaned the VERY dirty colour wheel by removing it, and using some Windolene and a cotton wool bud/cue tip, i used one end of the bud as the 'wet' end to gently scrub the wheel one segment at a time, then using the other end to immediately dry that segment until it was crystal clear before moving the wheel to the next segment, and then doing the same on the other side of the wheel.
I then used a tooth pick and a squashed bud/cue tip just to brush over the Colour Wheel Optical Sensor to make sure it was dust free, and checked the Marker on the Wheel, which was perfect.
After i replaced the wheel, i used a bud/cue tip to remove any excess lumps of dust from the fins of the heatsinks i could reach, and used a hoover nozzle to get out what i could.
I had no compressed air so i used short sharp blows to clear what i could, and put her back together again, giving all the vents one last go with the hoover...
Problem solved!.. No flashing/flickering/colour changing, just 100% perfect, and i didnt realise how degraded my image had become!
I run all my video through my Media centre, which serves the whole house for a number of functions, as well as being my Audio Workstation, and i had previously thought my Nvidia Drivers, due to a software issue/conflict, had been causing a slight banding on skin tone gradients and loss in detail which i have been trying to solve for months, and the Colour Wheel had been the cause!
Movies, Games, TV, all look much crisper! I'm still on my original bulb, and i would highly suggest anyone/everyone with a steady hand and an hour or so to spare to gently clean your Colour Wheels, especially if you've had it a few years like me! And its not as delicate as i thought it was going to be, just take your time...
Well hope this helps someone who might have been in the same boat as me.
Happy new year everyone, and happy projecting!