i suppose you installed Airnav on youre C: drive ( if not, change C by the letter of the drive where you installed it )
there you should see a map called AIRNAV SYSTEMS ( so this should read C:\AIRNAV SYSTEMS )
open this map, then you see a map called AIRNAV RADARBOX ( up to now the pad is C:\AIRNAV SYSTEMS\AIRNAV RADARBOX )
on opening this map, the first submap you see now in the list is COLOR, open this one, and there you see the .mcl files.
so the full pad to follow is : C:\AIRNAV SYSTEMS\AIRNAV RADARBOX\COLOR
the reason why i advise you to make a copy of the Real Radar.mcl as Real Radar original, is that so you keep a copy of the default program settings, any change you make out of personel preference you will have to export to the Real Radar file, as the program always starts-up with this setting ; so changing collors and saving under a different file, something like My Collors for instence, will always show the default ( Real Radar ) collors on start-up, and then you will have to load you're personal collor file to get you're collor settings.
ofcourse, IF you did not followed the advise to install Airnav in a other map than the default "PROGRAMS" folder, then you will have to start looking from C:\PROGRAM FILES\AIRNAV SYSTEMS\AIRNAV RADARBOX\COLOR, but if this is the case, i strongly recomend you to uninstall the program and reinstall it in his proper folder in C: ( ore whatever drive you want to put it on )
attached are 4 screenshots of what you should aproximatly see in every step
