[Alan] has been working on driving this WS2811 LED module with an AVR microcontroller. It may look like a standard six-pin RGB LED but it ... pixels with a 16MHz AVR chip. They use single-wire ...

A larger matrix like this 16 x 16 x 16 LED build, has a total of 4096. This would be a nightmare to drive with plain RGB LEDs, even with cunning multiplexing, but luckily you can buy indexable ...