Revenue collections by state government have been so surprisingly strong that officials now expect Colorado single-filer taxpayers will each receive refund checks of at least $750 this summer. That’s an upward revision from the previous May estimate of at least $500 per taxpayer, which itself was an increase from the amount of $400 per taxpayer that lawmakers and the governor announced in April. Colorado’s Taxpayer’s Bill of Rights (TABOR) requires the state to refund any tax revenue it collects above a cap calculated based on rates of inflation and population growth.