I realize that I've probably done this topic to death but I spent a lot of time last fall on ignition systems.
So, here are a couple of photos of sparks. I was trying to capture the visual difference between the CDI and induction style systems.
The first photo is with the LS2 coil and a surface gap plug. This photo is pretty close to what you see with the naked eye, the purple color is very distinctive.
This photo is with the RCEXL system driving a standard small engine plug with the electrode cut off. The resulting gap is enormous and none of the induction systems produce enough voltage to jump that gap even at atmospheric pressure. The CDI system delivers less energy per spark than the induction systems I've tried. The resulting spark is pencil thin and bright white.