Dual Lands and Color Identiy

I am a bit confused by the color identity of rules for Commander. I have an Overgrown Tomb. There are no mana symbols on the card. The Card Type is "Land - Swamp Forest". To me it seems like there's no color identity on the card, so it's colorless. The official rules website doesn't make it clear.

Can I include that card deck with a blue/black commander?