GGR for the month amounted to $17.2m (£12.6m/€14.2m), which was 6.5% lower than the $18.4m posted in November.
When taking into account adjustments such as bonus promotions and a 0.25% federal excise tax on sports betting handle, the decline was much greater, with net sports betting proceeds (revenue) for the month down 43.3% to $5.1m.
However, the situation was more positive in terms of handle, with consumer spending for the month reaching a record $284.6m, up 21.3% from the previous monthly high of $231.2m set in November.
Breaking down these figures, online remained by far the main source of income for licensed operators in Colorado.
GGR from internet betting stood at $16.6m and net sports betting proceeds at $5.1m, with players having wagered $280.4m online and winning $263.9m.