Kdawg is describing a custom track palette. Is that what you mean? I ask because I'm not sure what you question means.
> How do I utilize a custom texture in MTM2 that I've created?
Track, terrain or model texture?
For tracks, it's as Kdawg describes. You may create or indicate any palette you want to use from the menu in traxx. It's been a while but if I recall correctly you can do the same thing in tracked2 under the 'edit track details' option.
For terrain, textures are 64x64 tiles that you lay on the ground to create the sense of scenery. Custom and stock textures are used exactly the same way. But I know you've done this before.
For models, textures can be 64x64 or 256x256 in size. You have to use a unique name, and you must edit the bin model so that it knows what texture(s) to use. You can do this in binedit or you can repaint existing textures and use a texture replacer.
> Where do palletes come in?
Palettes provide color for RAW files. There's a few notes here.
http://mtm2.com/~mtmg/trucks/palette.html
If you need something more specific, please ask.