Okay, I found a REALLY hacky way to make this compatible with speed gel. It depends on being able to fire outputs when the player dies but before the map reloads, which I think a logic_playerproxy will let me do. The trick is that the gel-on-ground color requires a mapload to take effect, but the gel-on-player color changes immediately. When the player dies or finishes a test I'll switch the color to orange, then switch it to some sort of reddish purple as soon as the map loads.
Lasers would reflect off Adhesion Gel, but remember that Adhesion Gel only works on perpindicular corners. Reflecting wouldn't do much. 
I suppose I could also replace Conversion Gel with this and let people use Reflection Gel in the same map, but they'd have to be the same color on the ground. It would get confusing, and replacing Conversion effects would require a VPK addin.
This would only replace the Reflection Gel effects for a single map. If you play any map that doesn't have Adhesion effects paked into it, you'll see normal reflection gel.
I'm planning to make this into a custom gel eventually, but it's much less interesting than trying to get other testing elements compatible with the concept of Adhesion Gel in the first place. Yesterday I got it to play nicely with tbeams, bridges, lasers, and box droppers. But now the player automatically drops the box when they step on Adhesion Gel, which isn't good, etc. That's the part that's the most exciting to program, so I'm doing it first. Once I have almost total compatibility I can start to replace ithe paint sprayer gel with a custom blob.