Rainbow Ore is one of the game's resources. It is a rainbow colored ore refined to be used in tower construction (used to fortify defense towers). It's worth 1 gold. You can also send them to your friends in Facebook at level 10.
It can be obtained from
- Battles and Level Taxes within most of the Grasslands
- Supply Station
- Tavern (high probability, along with Earth Essence if you opt out of the Gold and Ham)
- Prison, at random when you capture a prisoner.
- Daily Grind Rewards, certain quest rewards
- Daily Login Reward (random, with a couple of 2)
- Daily Check (once a month)
- Online Reward
They can also be purchased with cash and/or diamonds at the Marketplace, when it is open.
There are two areas in the Grasslands that do not have the potential to provide Rainbow Ore, Canine Fortress and The Twisted Green. You can always verify what the potential rewards are by placing your mouse over the flag denoting the various difficulties at each location.
Rainbow Ore can be Synthesized into Quality Rainbow Ore at the Forge. You need to upgrade at least one kind of tower to level 31 before you can do this. After all your towers are at level 31 or more, and once all soldiers are upgraded to Tier 3, this is the only use left for this item.
The max stack of Rainbow Ores is 9999.