On my DLP projector I use to have it on a coffee table and was shooting up. I had to put a number of cup mats under the front leg to get a height I needed and correspondingly had to have the key stone quite aggerssive. I would see rainbows quite requently, espectialy when i was tired. I now have a stand so the projector is now head on (well pointing slightly down) and I haven't seen a single rainbow since doing this. Non of the people I live with have either, although they rerely saw any unless I reminded them that they exist. So does the angle of the projector/keystone make a big difference or have I just become imune to rainbows over time?