|eeZee RGB WS2812B breakout board on Tindie|
There's a much lighter-weight library for driving these LEDs that's perfect on memory- and flash-limited ATtiny AVRs -- or really any AVR for that matter.
All you need is the light_ws2812 library. I'm using it with the ATtiny25 on my eeZee RGB test jig.
Adafruit gets all the attention, but this little library is small, easy to use, and works great; it deserves more press. Pass it on, k?