1- Recruitment is in the export_descr_buildings.txt. It is very complex and very hard to edit by hand. Take a look at it (lower half of the file), if you've never modded the files before it could give you a heart-attack.

2- Color changes are done in the descr_sm_factions.txt. Change the RGB values in the primary and secondary colors under the faction's internal name.

3- Skins would be under the descr_model_battle.txt. Just look for the section for the unit you want and switch info on the lines for the factions you want to change.

Note 1:
Always backup your files before making changes because mistakes are always bound to occur.

Note 2:
Remember that internal names and the factions' ingame names don't always line up. For example, "seleucids," is actually the Romani faction.