Most of the time, it's just the blue LED-ghost from Ikea, but when I've just finished a project, I leave that running -- those high-powered LEDs give a pretty good illumination in the dark (and shironuchan can attest to that!).
So when I had finished the three color-changing RGB LED-thing, I left that out. When she got back (this was the first time she saw it working), klik grabbed her Colorsplash camera, and took some photos.
If you look closely, you see the 'streams' of light change color a few times.
Look at the blue line at the bottom right -- it seems as if it is a dotted line. This is the PWM: each 'dot' is when the LED lights up fully, the rest is merely the (less bright) afterglow. The human persistance of vision makes that the colors 'mix'. This is how you can produce the colors via Pulse Width Modulation.
Another one. Again, a few color changes can be seen. It also shows quite nicely how the 'white' works.