Any company that operates as a sportsbook must be licensed, which requires them to pay a fee of $10,000 to the state of Colorado, as well as a licensing fee of $125,000. They also pay 10% tax on all gross gaming revenues made each year.
With regards to player winnings, they are taxable – you will be given a W-2G form if you win more than $600. You can declare gambling losses as a tax deduction on the provision that you declare gambling wins as income. Your losses cannot exceed your winnings, though.