Colorado once had a registration 'tax' but finally figured out that it was costing the state more money to administer the program than it brought in as revenue, so they dropped it.
The much better 'news' is that some years back, Colorado tried to lure United into building a major overhaul base in the Denver area. To sweeten the bid they removed the sales tax on aircraft parts. The bid failed and United built their overhaul base elsewhere. But the law remains on the books, and home builders can claim tax exemption on their airplanes. My first plane was registered with the FAA and the state did nothing. When the second plane I built was registered the state picked up that information (as most states do) and wanted sales tax on the cost of the plane. I sent them well over one pound of receipts, shipping documents, and supporting information like local sales receipts, and they backed down. Amount saved was several thousand dollars.