has to do with the color wheel of a single chip dlp projector...
basically, a dlp is made up of lots of itsy bitsy iiny tiny polka dot bikinis...no actualy they are tiny tiny mirrors...
these little mirrors reflect light through a color wheel that spins really really fast to create an optical illusion to make your eye see different colors...basically blending them...
however, on some material and with some people, when there are movements, they can see a rainbow of colors very briefly, to some of those people it can cause naseau or headaches...where this is most prevalent is with slower wheels (1x and 2x) and where light and dark clash...with faster wheels 4x and 5x there are very few people that experience this...
here is a link with an explanation for ya.
http://www.hometheaterhifi.com/volum...er-7-2003.html
Especially when it's a dark scene with a few spots of light. But the rainbows don't bother me as much as the internal reflections, but that's another story... 
