While Colorado doesn't charge property tax, they do assess a use tax for some airplanes brought into state, and registered in Colorado.
If you build an experimental and register it in Colorado, there is no tax. That is because it is considered "parts", and they are exempt because of a ruling permitting the exemption of parts because of an allowance to United Airlines.
If you bring a previously registered experimental into the state, it is taxed the same as a factory airplane. I'm not sure how they would treat an experimental if you are the builder, and had previously registered it in another state.
Roger Bloomfield
N51BL RV-8 at KAEJ (Buena Vista, CO)