You owe use tax to Colorado when you don't pay sales or use tax with a purchase that you intend to use, store, distribute, or consume in Colorado. You can see if you paid sales tax on a purchase by looking at the purchase receipt. Some online purchases have sales tax already included.
Generally, use tax doesn't apply to items that are exempt from Colorado sales tax when you buy them in Colorado.
For additional information on Colorado's use tax, see FYI General 10 .