Thanks!
I now did the following:
- follow link, unpack
- open Rainbow_CMD_V2_0 with Arduino 0017
- compile (resulting sketch size 5688 bytes)
- connect SparkFun AVR Pocket Programmer to Rainbowduino -> PWR LED is green.)
- avrdude -c usbtiny -p m168 -U flash:w:Rainbow_CMD_V2_0.cpp.hex
- lights flash, verfy is OK.
- disconnect programmer
- attach external power supply, pwr LED green
- press RESET, reset LED red.
- remove power
- add LCD matrix (square pin in round hole).
- reattach power supply -> pwr LED green.
Still nothing happens…
I’ll probably do something wrong along the way 
Best,
Jens