I know exactly what you mean and, no, as of right now I don't think there's a way around it - you either change the main file or you don't. I decided not to.
The devs have made the engine color function off a simple RGB number specification mechanism so clearly the capability is there to do it that way for everything. They just didn't do it. I haven't the slightest clue why we aren't able to specify colors directly in the GUI in that way. The gradientmaps strike me as a really stupid solution to a problem that shouldn't even exist in the first place.