Did the readme include a section to be copied and pasted into the aircraft.cfg?
Without a [fltsim.X] section for the livery there, the sim doesn't know it exists. The author generally includes it for a repaint.
The following should help you understand what should be there.
There are other lines that can be used, this was handy...Don
title=falcon50 CAEA NC Title MUST be completely unique throughout the sim
sim=falcon5X Name of xxxx.air file, preceding the dot-air
model=cv Model folder extension, after the dot
panel= Panel folder extension, after the dot
sound= Sound folder extension, after the dot
texture=caea Texture folder extension, after the dot
kb_checklists=Falcon5X_Check Checklist, can be htm, txt, etc.
kb_reference=Falcon5X_Ref Kneeboard Reference " "
atc_id=808 Details tab, Tail Number
atc_airline= Details tab
atc_flight_number= Details tab
ui_manufacturer=Dassault "Mfg" in the dropdown These three lines are the text you will see when
ui_type=Falcon 50 Selecting the plane from the menu
ui_variation=CAEA No Cabin
ui_typerole=Corporate Jet "Type" in the dropdown
ui_createdby=Falcon Team "Publisher" in the dropdown
description=Dassault-Aviation Falcon 50
/nOriginal FS2K/2K2 version by: Yannick Lavigne, Fred Banting, Rob Young Falcon 50 colors
/nUpdated for FSX by: Ludovic "vonstroheim", Philippe Wallaert, & Don "fxsttcb" Bodenstedt
/n December - 2010 Details tab
 Sorry Alex!! I was digging the above out of my archive and got distracted...Don