If the original color was created based on one of the "Library Colors", like Pantone or so, the situation is different.
Inside the maker.ini, section [Preferences], you'll see a setting
GetLibraryColorRGBFromCMYK=Printing
Try setting this to
GetLibraryColorRGBFromCMYK=None
and restart FrameMaker. Of course, the color you specified is indeed very dark and puts a lot of ink on the paper, you might just try to adjust the values?
- Michael
[Edit: There are two maker.ini files, one in the program folder, the other in your profile directory!]