No idea why the image is 124x124, but having a 2px 100% transparent 'border' around the original 120x120 image works. Designers: don't forget the image has to be pre-masked with the icon shape.
The image is loaded as a mask to the icon backdrop, rather than in the image's actual form. Whatever is loaded in there will act as a monochromatic mask, meaning I can't theme the beta Activator icon.
There is a solution, though I can't remember entirely how I did it. Unless Petrich adds a switch to turn on/off the new icon style, this fix will have to do. Go to:
/Applications/Activator/
and open Info.plist, you'll find a key/string referring to the icon style. Delete the whole thing and respring.
It might be a different file, located somewhere else. You might have to do some searching around. Sorry I can't be more helpful!