I would recommend the Extended Spawnmenu add-on to copy/find the materials.
Many of the materials can be coloured with the colour tools or E2 code. If you see it in bright green in the pictures, it can be coloured.
[AAR reporting mark]/*
- Australian Railroads
- UK Railroads
/*- Japanese Railroads
materials/models/logos/companies/*- Non-Railroad Companies
materials/models/logos/misc/*- Things that are neither companies nor railroads
More will be added over time, and the crap-looking stuff will be upgraded. It's a process.