Common/standard library and/or protocol for Arduino to be I2C slave for driving NeoPixel
You should break your project up into smaller parts.


Consider using other led strips, that can be driven directly. Consider using ready-made parts or opensource code (google).
Make an Arduino drive a NeoPixel Ledstrip. (Check adafruit libraries/NeoPixel guide)(Sanity/wiring check)
Communicate with Arduino and Beaglebone over I2C. Try sending "Hi" and respond "Ok".
Think of a protocol, how to indicate start/stop of a message.
Send the "color bytes" using said protocol.
Unpack the color bytes and put them in a pixel array (See NeoPixel library).
Run "ledstrip.show();”


Please atleast try to do these steps. If one fails, you can create a question with details on what you have tried or what isn't working.

Maybe "nodepixel" already has the Arduino code for you. You then only need to know what bytes to send over I2C, which you can do with any programming language that supports I2C access on your platform.