Ok, so eventually FFG is likely to release new major factions in addtion to the smaller "neutral" houses... you know the one's with an actual claim to a crown. So what colors should they be? An important thing for those not choosing to paint their armies.
Stark is Whitish grey and Lannister is red fitting their colors from the books. And neutral is brown, which is a smart decision given war machines and ships if they come out are likely to be neutral as well.
But what next?
My choices:
Baratheon: Yellow is obvious but sorta bright and ugly. Especially when you have Lannister and Baratheon fighting each other which they often did. This could be a bright mess giving a ketchup and mustard effect.
My choice: A yellowish green. This tones down the yellow and covers both Renly and Stannis.
Greyjoy: This is pretty easy really. Either a dark grey which would still contrast with Stark or a blue.
Targaryen: This one is tough. Red is already taken, I'm not sure purple would look good, and black may be too dark? If Greyjoy is blue they could go with the dark grey here.
Night's Watch: If they're going to do a black they'd almost certainly do it here.
Others: A light ghostly blue that makes you think of winter.
I'm not really sure if the other factions would just be neutral houses so for now I'll leave it there.
Love to hear your thoughts. Plus we'll be able to look back later and see who called it.