Some time ago I wrote an online Gerber file viewer. I’ve been using it to validate the KiCad Gerber output files, before I sent them to the PCB manufacturer. One feature that was missing was the ability to set transparency on the layers, when more than one layer is selected for display.
As I started working on that, I realized that I also need to be able to select the color for the layer as well. Here are a few screenshots of the viewer in action.
Two layer PCB, top layer is red, the bottom is green:
Six layer PCB (Beagle Bone XM) with top and two internal signal layers selected:
The same Beagle Bone XM board with 6 layers selected: