Do the m15 lands have a default activated ability. I would assume it gets tapped for colorless unless the player needa the color mana.

Yes, the default is to tap for colorless mana, if nothing indicates otherwise.

If a player wants to cast Polukranos, World Eater using a Forest, a Llanowar Wastes and two lands that can't produce G, then they clearly had to use the 2nd ability of Llanowar Wastes, and need to take 1 damage; if they don't announce that change in life totals, we need to step in (GRV for not resolving that ability correctly).

d:^D