Thanks Headrush.
I see now how the LED Blinky Controls Editor works. Normally, "Colors.ini" is used. But if there's an entry for the same game in "LEDBlinkyControls.xml" (updated by the Controls Editor) then that gets used. Sounds great, but no matter what I set, I can't get the trackball to light up for a game. I've set it as Primary Control too (in "common"). Still nothing. Heck, it even lights up in the Controls Editor when I use "Test RGB LED". I've looked at the documentation, but it talks more about joysticks than trackballs - and nothing seems applicable.
Arrrggh!