A DMD has no inherent colour capability - it's just a configurable mirror
array. If you want to do full-colour projection, then, you'd expect that
you'd have to use three DMDs and three coloured filters - red, green and
But if a single DMD's switched in synchrony with a rotating "colour wheel"
- a spinning tri-colour filter that lets through red, green and blue light
in turn - then the very rapid switching speed of the DMD lets it lay down
red, green and blue images in such fast succession that the result is a
perfect colour image.
You can do the same trick with a single LCD panel, but it's not a good
idea; LCDs are transmissive, rather than reflective, devices, and block
something like half of the light that tries to get through them. To maximise
brightness in LCD projectors, a three-panel design works better. If you
try to pump the entire output of a super-bright lamp through one LCD, keeping
it cool becomes rather challenging.
The extreme smallness of the moving parts on a DMD mean that it behaves
like a solid state device, not a mechanical one. For all their complexity,
DMDs have very high Mean Time Between Failures (MTBF), and well-made projectors
based on DMDs can be expected to last easily as long as LCD units, and probably
longer. If a DLP projector fails, it's not at all likely to be because there's
something wrong with the DMD.