where in their quest line do you get it?

got MM and RR straight away, and just had to wait for the prydwen to turn up for the BOS one

i though i read somewhere its the quest reward for winning game with institute, is this true? do you actually have to complete the game with institute to get it? (unlike the other 3 factions)

Yes, you have to win the game with the Institute to get the X-01 paint.

stink

thanks

It does, and I'm pro-Institute. You should get it after the Libertalia or Bunker Hill quests, not as an endgame goodie.

There is always http://www.nexusmods.com/fallout4/mods/4847? mod, which allows Institute paint for all armor types. I honestly don't know if you actually have to unlock the paint through play or not, but the other power armor models also look cool with Institute paint. He also did the Minutemen and Railroad.

thanks but xbox cant use mods (yet anyway)

Yeah it's really crappy that you can only have the paint (normally) by beating the main quest. I didn't know that at the time and naturally did just about everything else in the game before hunkering down for the main course. Naturally though after completing the storyline, I had no motivation to continue playing and started a new character to see other faction endings.