Check out File > Examples > DigisparkUSB to see the DigiBlink example - it controls an RGB LED over USB just like you say.. You need to have a program on the PC to connect to it and write out rgb bytes. I believe there\'s an example for doing this with python mentioned somewhere in the forums. It\'d be nice and easy to do with ruby too using the digiusb rubygem if you\'re at all familiar with ruby. Here\'s an example of talking to DigiBlink sketch in ruby:
# a ruby program for making a digispark with rgb shield running digiblink turn purple
require \'digiusb\'
light = DigiUSB.sparks.last
light.putc(115) # start character
light.putc(255) # red value
light.putc(0) # green value
light.putc(255) # blue value
I don\'t have an RGB shield though so I haven\'t tested this. Should work though! It\'s a pretty simple program. :)
Anyone want to test if this example works? If it does, I\'ll add a more comprehensive version to the examples folder in the digiusb rubygem.