New to Commander…help me understand.

I got the Dance of the Elements precon, which is a WUBRG deck, but the commander, Ashling the Limiless, is only a 1 Red/2 any color.

I thought that the deck couldn’t contain colors that the commander didn’t have, so I don’t understand how it would work. Can someone explain why this red commander would work with a WUBRG precon?