Perhaps this is a shortcut to get other colors out there quicker. The original is awesome. But we all want a custom one, so for the Photoshop educated check this out:
nvi utilities. Its a script that breaks the .srf into a png that you can edit, and then you can put the .png back as a .srf
I changed the car color to orange and put it back together as a .srf. I don't have a Garmin so I can't do any testing to see how this works.
I'm not taking requests to make colors, I just wanted to put this tool out there to help the color process.