It's been a dream of 3D printing hobbyists to be able to print in glorious color. That dream still is developing, but maker RichRap has taken a big step in that direction by developing a 3-way extruder for RepRap-style 3D printers.
It's not exactly a full color 3D printer, although RichRap's initial intentions were to mix filaments to create arbitrary colors. He found color mixing was difficult and did not produce the most interesting results. He says:
I decided that not mixing the colours well would produce more interesting effects and give more artistic looking prints. So during #30DOC in June I restarted the development and added three feeder tubes. I had initially intended these to be separately driven Cyan, Magenta and Yellow feed, but after some testing realised that all sorts of blends could be made by running single or multiple extruder’s at intervals separately or together.
Thus he proceeded with building a single extruder capable of accepting up to three separate filament inputs. The resulting prints are indeed startlingly colorful, as you can see with the Froggy model above.
RichRap has made the plans for this extruder available on Thingiverse for all to try.
While able to produce very colorful models, this is not the "true color" 3D printer some have sought. But we're getting more hopeful every day.