Colorado's proposal to replace its flat income tax with graduated rates will remain on the November ballot for now, after a Denver District Court judge rejected a legal challenge on Wednesday and the challenger appealed to the Colorado Supreme Court on Thursday, according to Colorado Public Radio. Denver Focal also reported the ruling and the planned appeal on Thursday.

Source: Colorado Public Radio

Amendment 87 would raise income-tax rates for the state's wealthiest residents and lower them for most others. If it passes, the measure is expected to raise an estimated $2.7 billion a year for the state, with the dividing line between households that pay more and those that pay less at about $500,000 a year. A rival measure, Proposition 136, would cap the income-tax rate at 4.4 percent.

Judge Heidi Kutcher ruled that the challenger, Michael A. Hancock, did not meet his burden of showing that petition organizers' registration practices or alleged training gaps violated the law in a way that would invalidate signatures. Hancock had argued that signatures collected by 69 paid circulators — more than 11,000 in total — should be thrown out. State officials certified 130,938 valid signatures for the measure, only modestly above the 124,238 required.

Key numbers

130,938 valid signatures certified; 124,238 required; more than 11,000 signatures challenged; an estimated $2.7 billion a year in new revenue if Amendment 87 passes.

"We appreciate the Court's careful consideration of this matter, and look forward to voters making their voices heard on this question," Colorado Secretary of State Jena Griswold said in an emailed statement after the ruling. Chris deGruy Kennedy, co-chair of the Protect Colorado's Future coalition behind Amendment 87, said the group was "elated and relieved" by the decision.

Hancock's attorneys, Jason R. Dunn and David B. Meschke of the Denver firm Brownstein Hyatt Farber Schreck, argued in the appeal that a number of petition entities did not register paid circulators as required and that the signatures those circulators gathered "must be invalidated." The appeal asks the state Supreme Court to take up the case on an expedited basis, with Election Day about 13 days away on November 3.