Along with changing the textures to your new one, you must also modify your aircraft.cfg file to show the new plane or livery. This is an example from the Fs2002 737 to show you how to do it:
   [fltsim.0]
title=Boeing 737-400
sim=Boeing737-400
model=
panel=
sound=
texture=
kb_checklists=Boeing737-400_check
kb_reference=Boeing737-400_ref
atc_id=N700MS
atc_airline=American Pacific
atc_flight_number=1123
ui_manufacturer=Boeing
ui_type=737-400
ui_variation=American Pacific Airways
description=One should hardly be surprised that the world's most prolific manufacturer of commercial aircraft is also the producer of the world's most popular jetliner. The 737 became the best-selling commercial jetliner worldwide when orders for it hit 1,831 in June 1987 (surpassing Boeing's own 727 as the previous champ). However, it wasn't always that way\s in the first few years of production, there were so few orders that Boeing considered canceling the program. They didn't, and the airplane has more than proven itself in over three decades of service.


[fltsim.1]
title=Boeing 737-400 Paint1
sim=Boeing737-400
model=
panel=
sound=
texture=1
kb_checklists=Boeing737-400_check
kb_reference=Boeing737-400_ref
atc_id=N700MS
atc_airline=Landmark
atc_flight_number=1123
ui_manufacturer=Boeing
ui_type=737-400
ui_variation=Landmark Airlines
description=One should hardly be surprised that the world's most prolific manufacturer of commercial aircraft is also the producer of the world's most popular jetliner. The 737 became the best-selling commercial jetliner worldwide when orders for it hit 1,831 in June 1987 (surpassing Boeing's own 727 as the previous champ). However, it wasn't always that way\s in the first few years of production, there were so few orders that Boeing considered canceling the program. They didn't, and the airplane has more than proven itself in over three decades of service.

[fltsim.2]
title=Boeing 737-400 Paint2
sim=Boeing737-400
model=
panel=
sound=
texture=2
kb_checklists=Boeing737-400_check
kb_reference=Boeing737-400_ref
atc_id=N700MS
atc_airline=Orbit
atc_flight_number=1123
ui_manufacturer=Boeing
ui_type=737-400
ui_variation=Orbit Airlines
description=One should hardly be surprised that the world's most prolific manufacturer of commercial aircraft is also the producer of the world's most popular jetliner. The 737 became the best-selling commercial jetliner worldwide when orders for it hit 1,831 in June 1987 (surpassing Boeing's own 727 as the previous champ). However, it wasn't always that way\s in the first few years of production, there were so few orders that Boeing considered canceling the program. They didn't, and the airplane has more than proven itself in over three decades of service.

With this setup you should see the aircraft in the Fs2002's window and when you expand it your new livery should be listed.
Hope this helps.

???Hi,
This has happened to me. I d/loaded a Bae146 with Air Uk and Buzz textures, altered cfg. etc as normal, they show in select aircraft panel, but when Air Uk is selected it is in Buzz livery on the r/way ??? ??? ???. Checked and double checked, but I can't suss it yet,  HELP.
Here's hoping,
Tony C.

Did you install the paint in as a new texture or another aircraft? If it is another aircraft, but shares the same title in the aircraft CFG it will go to the default and then you will have to select it in game.
For instance, say you install another bell206 as a new aircraft and use the same aircraft CFG as the bell and add the new entries to it except for the original title, it will show up in the menu fine, but the only way to select it is during flight.