Spiritmonger's last ability causes it to become only the chosen color. It will no longer be the colors it was previously.

Spiritmonger can regenerate even if it isn't in combat, it's already tapped, or it's undamaged.

Activating the regeneration ability creates a replacement effect that acts like a shield, replacing the next time Spiritmonger would be destroyed that turn. This shield works against effects that try to destroy Spiritmonger or lethal damage that would be dealt to Spiritmonger.

You can activate the regeneration ability even if Spiritmonger isn't at risk of being destroyed.