I am currently working on this same problem. I need the word "FIRE" in white letters. Tried to print the word using a text box in Photoshop with no background, but it came out red, so I screwed up. I'll keep trying and let ya know if I come up with anything.
Chris
edit: Went back and tried again. I went ahead and used the red background and the text function to put the word in white on it. The red matches pretty well to the red fire alarm call box I am putting the word "FIRE" on; good enough for me anyway. Chris, if you can manage to match the background color in Photoshop to your Vomit Comet well enough, you may want to give this a shot.