Use an RPF manager, like OpenIV, to modify game files. 
ALWAYS use OpenIV's "mods" folder feature!
ALWAYS make backups of your files before modifying them!
NEVER play GTA Online with modded game files!

1. Copy "x64e.rpf" and "update/update.rpf" to your MODS folder, if they aren't already there.

2. Replace files in "mods/x64e.rpf/levels/gta5/vehicles.rpf":
	freight.yft
	freight.ytd
	freight_hi.yft
	freight+hi.ytd

3. Replace files in "mods/update/update.rpf/x64/data":
	carvariations.ymt

4. Launch GTA 5 and wait next to train tracks.

IF for any reason you have another mod that modifies "carvariations.ymt", you will need to modify it yourself to make the train spawn with the correct colors. Follow these steps:

1. Open your own carvariations.ymt file in Edit mode.

2. Search for the <Item> which has <modelName>freight</modelName>.

3. Just below that model name, you'll see an <indices content="char_array"> entry. Replace it with:
<indices content="char_array">
126
46
3
156
0
0
</indices>

4. Save the file and exit.

