When I launched HoudahSpot this morning, the program's auto-update feature told me that there was a new version available, and listed the new version's bug fixes and added features. One of the last features caught my eye, as it's one of the things about HoudahSpot that I didn't like: you can now set the field header background color via a hidden preference. Just enter this command in Terminal (after quitting HoudahSpot):
defaults write com.houdah.HoudahSpot accentColor color_to_use
Replace color_to_use with one of red, green, blue, grey, or yellow (the default). Relaunch HoudahSpot, and you'll see your newly-chosen header colors. Hopefully a future release will bring a true pref with a color wheel to set the title bar background colors, but this is a usable workaround for now.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080414050326715