What color are Nissa, Worldwaker's lands?
Normally lands are colorless (there is currently only one exception). Nissa does not assign a color to the lands she turns into elementals, so they would remain colorless.

Also worth noting, there are no tokens created. I am not exactly sure what you mean by this. What happens when you use Nissa's ability is that a land becomes a 4/4 Elemental creature, while also retaining its previous properties as a land (tapping for mana, having the "Land" type, etc).