After extensive troubleshooting of what I believed to be was faulty cables, I've redone all the cables except the powercables in the machine. Now everything is nice and pluggable/unpluggable in a easy manner.
The problem wasn't in the cables however, but the cabling still needed some work.
When I tried a different version of the digitalWriteFast it, for some peculiar reason, broke the pins I was using so I tried plugging the display into another set. The refresh rate of the screen was becoming rather slow and at that time I didn't connect that those pins were not "accelerated" by digitalWriteFast.
Also - the new library was approximately 1.5 x slower than the old. Doh.
So anyway - I reverted to the old library and the old pins and now my code could do its work properly.
|1) Multicolor display. Four different reds and one black layer.|
Here it's simply displaying f(y)=red, but any pixel can be any shade.
I will do further testing with SPI enabled since I need to get the time needed for each update to a lot less than it is currently taking. It is currently updating a full 4+1 color frame at 19 ms, which is "really slow". I hope to get this down to under 1 ms, if possible...