Guys, the issue here isn't that there is any ban or legal reason to not ship to Colorado. Just because one if you will, doesn't mean everyone will.
I can legally buy, own, and carry, any ammo I want here in Connecticut, I can legally buy and own and carry a 10 round magazine for a pistol,,,, but there are companies/business that have said "screw you," to any customers in any states with what they see as restrictive gun laws. I have had several companies/businesses refuse to ship any firearm related items to Connecticut even though those items are perfectly legal here.
Those companies often have a list of states they will not ship anything to. Colorado may very well be one of those states that some, not all, companies/businesses will not ship gun related stuff to.