While it doesn't hurt to try, reinstalling UMM may have no effect at all. It changes the colors of buttons by modifying values in either App or MainMenu (or both, can't remember correctly), and not by changing anything in any of the scripts from the scripts\Icons folder...
But in KM1 some of those scripts (in the Icons folder) are indeed changed. Dunno exactly which ones tho, but I remember the RacesIcons.py for example isn't a stock script.
Try going thru the packs of all mods you have installed, and in the order you installed them, and re-installing the scripts they place in the scripts\Icons folder. I know that might be a little pain-in-the-ass job, but chances are, most of the mods you have do not put anything in that folder.