What could be improved on?
1. Shading around the edges.
As we all know, most commersial airliners are round. The very best way to simulate something round on a flat immage is by shading around the edges. Without shading, the aircraft looks very flat and not really that colourfull either.
2. Colouring in wherever it's needed.
If you take a good look at the livery itself, you may notice a few "white spots" not only around the edges, but also around the "wing cartridges", elevator, back door, back "exhaust pipe", e.t.c. You can remove these by colouring them in a similar colour scheme of what is around them. This is to make the plane look as real as possible. Look at some other liveries up close to get a good idea.
3. Perfecting the dimensions.
The livery dimensions AE uploads in is 800x300. Looking at your livery in your airline details page, it looks very squashed horisontally/stretched vertically. Try making any future liveries in 800x300 or anything similar to that in order to prevent squashing or stretching.
That's all the things I found you can improve on and I hope this helps
Ps. I'm not an expert on airplane parts.