A ballot measure headed to voters in November is asking Coloradans to forgo tax refunds to improve teacher salaries and shrink classrooms. Supporters and opponents disagree, however, on whether or not the measure would count as a tax increase — and whether it would be an efficient use of taxpayer money. Proposition NN — referred to the ballot by Democrats through Senate Bill 26-135 — asks voters whether the state can retain and spend up to $4.6 …