The spending targets Amendment 87 and Proposition NN, which would direct billions of dollars toward public services. Amendment 87 would create graduated income tax rates for businesses and individuals, increasing taxes on people earning more than about $500,000 and raising an estimated $2 billion in its first full year for health care, education and child care. Proposition NN would redirect potentially billions of dollars in future Taxpayer’s Bill of Rights refunds to K-12 schools and early childhood programs for at least a decade.

Four committees are opposing the measures: Don’t Price Us Out, Brighter Colorado, the Americans for Prosperity Colorado Issue Committee and Keep Colorado Affordable.

Don’t Price Us Out received $760,000 on Sept. 29 from the American Prosperity Coalition, a group with no online presence whose registration lists a Texas shipping store as its address. The committee also received $300,000 from Ready Colorado, a conservative education nonprofit that does not disclose its donors. Both organizations are among the groups commonly described as “dark money” because they do not reveal the sources of their funding.

The committee also received $25,000 apiece from Joe O’Dea, a Colorado construction company owner and 2022 Republican U.S. Senate candidate, and retired construction executive Jeff Keller. Don’t Price Us Out spent more than $800,000 on advertising at the end of September, including online ads opposing Amendment 87.

Brighter Colorado, which is also backing six conservative ballot measures, had raised nearly $3 million through Tuesday morning. About $1.75 million came in September from Common Sense America, a national conservative nonprofit that does not disclose its donors. Brighter Colorado also received $500,000 from the GOPAC Election Fund and $100,000 from Colorado Dawn, another nonprofit that does not disclose its donors. Because the committee is supporting and opposing multiple measures, its filings do not make it easy to assign all of its spending to particular campaigns.

The Americans for Prosperity Colorado Issue Committee had raised and spent about $350,000 opposing Amendment 87 through Tuesday morning. Keep Colorado Affordable is also campaigning against the measures.

Supporters have raised substantial sums as well, though some backing groups also keep their donors private. Protect Colorado’s Future Coalition, which supports Amendment 87, had raised nearly $2 million. Its largest reported contribution was $500,000 from Merle Chambers, a major Democratic donor and former oil and gas industry employee. Other contributors include education and policy organizations, some of which disclose at least some funding sources, while others do not.

Yes for Colorado Kids, which supports Proposition NN, had raised more than $5 million through Tuesday morning. The National Education Association contributed $3 million; other major donors included Gary Advocacy, the Colorado Fund for Children and Public Education, the Rose Community Foundation and CLCS Action. The money has funded a television and digital advertising campaign.

The competing campaigns illustrate how difficult it can be for voters to trace the interests behind political advertising. Some organizations report large contributions but do not identify their own funders, while other donors — including unions, foundations and individuals — are named in filings. That mix of disclosed and undisclosed money is shaping debate over tax policy and how Colorado funds schools, health care and child care.