As a house, you guys should decide upon the most common hair colour(s) and eye colour(s), but pretty much anything is fair game, save for platinum blonde or flamboyantly dyed hair. Platinum blonde is Targaryen, and none of you will have Targaryen blood. Not through being [&@%!] or [&@%!] of [&@%!], yeah no. Tyroshi love brights, and will wear flashy clothes, and dye their hair and beards in blues, greens, reds, etc. Would not recommend. Bit of a social stigma, as one might expect. Too garrish, and you'd be seen as Tyroshi, not Westerosi.
Purple eyes are PROBABLY a no-no, as well. Indigo, lilac eyes and the like are traits found in people of the blood of Old Valyria--so, once again, Targaryens. House Dayne had some purple eyes, too.
But any other hair/eye colour is pretty much fair game. Up to you guys. Maybe there was some mingling with a [&@%!] born in the Westerlands, and someone got passed down some shiny Lannister goldilocks. Or some Riverlands blood--Red brown hair, blue or green eyes. Northerners? Black/brown hair, brown eyes, green eyes. Maybe ancestors from Dorne, or across the Narrow Sea. Curly hair. Long hair. Straight hair. Whatever, really. Go nuts, excepting for those few exceptions.
