Class 377 - Gatwick Express
Based on Class 387 Gatwick Express red livery. Featuring a custom-made GX logo, made using basic shapes in Livery Editor.
This is the exact same livery as the one that I made for the Class 375. Apparently you can open the .tsw2liv file using Notepad++ and change the entry for the rolling stock directory to Class 377 from East Coastway and have it working in-game and in Livery Editor.
Import the .tsw2liv file using TSW2 Livery Manager
If you can't select any liveries for the Class 377, install this mod 377 Livery Fix.