James: Thanks for the link, and was an interesting read! Certainly put me in the right direction.
However, what I've noticed after uploading the newest communicator sketch, is that the problem seems to be in the length of the cables.
The length of wire between the blinkm and athe arduino is a little over 1m. And while the voltage signal is happy to carry that distance, it seems that the data to control the light gets lost.
When using shorter cable of about 10cm, the data gets through fine, and the light is controllable...
Consqeuently, is there any way to boost the 'data' signal? (perhaps wrong terminology...). If not, I'll be re-designing my project to house the arduino closer to the light source!