On Thu, 06 May 2010 01:20:36 -0500, mister_friendly wrote:

I keep seeing these little solar power sidewalk lights. Last year they
were all white (blueish white). Lately I see them where they change
color. Yet, they only have one LED. How can a LED change color? I
thought the color was determined by dopeing it with a metal. So how can
they change? This has me puzzled.

They could be RGB leds. These devices, now very cheap on ebay, are
externally identical to an ordinary two pin led though they contain three
emitting diodes in the same package plus a small circuit that flashes
each of them independently.
http://www.youtube.com/watch?v=PPtg4mFC_-k