Legal requirement in Colorado for days notice before raising rent

[Ken R.]

We own a number of rental properties in Boulder County, Colorado. All of our leases are for one year. Currently, 60 days before a tenant's lease term expires we decide if we would like to extend an offer to the tenant to sign a lease amendment to extend her lease for an additional year. Along with the offer to extend we might also inform the tenant what her new monthly rental fee will be (e.g., perhaps $25/month higher than it was during her initial one-year lease term). 

In reading some previous posts, it seemed that Colorado might require a 90-day notification period for raising rents. However, it wasn't clear if that was only for tenants on a month-to-month lease without a defined lease termination date (which is what our leases are based on).

I would certainly appreciate any insight on legal requirements surrounding notice period on raising rents in Colorado.