Outside groups stepped up to buy more than $5 million worth of the nearly $7 million in new political TV ad contracts last week.

Ads purchased by outside groups make up more than $38 million – almost 77 percent – of the total spending so far in Colorado.

Political ad buys total $49.8 million through Aug. 22 at TV stations in Denver, Colorado Springs, Grand Junction and Durango. The buys include more than 58,000 advertisements that are 30-seconds in length– the equivalent of 20 days of TV viewing.

These are just the ads filed with the Federal Communications Commission by traditional stations. Ads run on cable or satellite TV don’t have to be reported to the FCC.

New ads this week include $1.9 million for more than 1,000 spots by >Crossroads GPS,  a group closely associated with Karl Rove, the former adviser to President George W. Bush. The new buys, which began last week and are scheduled to run from mid-September through mid-October, bring the group’s total ad spending in Colorado to $3.6 million.

The Republican Governor’s Association spent just more than $1 million to begin airing ads in the race between incumbent Democratic Gov. John Hickenlooper and GOP opponent and former U.S. Rep. Bob Beauprez.

The group scheduled ads through mid-September. Its first ad plays off Hickenlooper’s recent game of pool with President Barack Obama.

Who is paying for the ads by many outside groups isn’t always clear.

It’s the difference between “dark” and “disclosed” money – and even when disclosure is required by state or federal laws, the money may still be difficult to trace.

The biggest outside ad spenders so far in Colorado are the Senate Majority Political Action Committee at almost $5.7 million and the Democratic Senatorial Campaign Committee at about $5.2 million. The two groups have ads scheduled through Election Day.

Those two groups are supporting incumbent Democratic Sen. Mark Udall and targeting his GOP opponent, U.S. Rep. Cory Gardner. Both are registered with the Federal Election Commission and must report their donations and spending to the FEC.

Senate Majority is a super PAC, which may take unlimited donations such as the $5 million each that billionaire businessman Tom Steyer and his NextGen Climate Action Committee, another super PAC, have donated.

The DSCC is considered a political party committee PAC, and may take donations of up to $32,400 from individuals and other committees.

Crossroads GPS, on the other hand, is among the “dark money” groups. As a 501(c)(4) nonprofit, Crossroads doesn’t have to disclose where its money came from. It doesn’t have to disclose all its spending, either.

Crossroads is running ads critical of Obamacare and Udall. Earlier this year, the League of Conservation Voters, another nonprofit that doesn’t disclose donors, ran ads critical of Gardner.

The ability to track TV ad spending is one of the ways to see how much Crossroads, the League of Conservation Voters and similar nonprofits are spending.

Then there are groups in which the distinction isn’t so clear.

The Republican Governor’s Association is a national 527 nonprofit that reports donations to the IRS but not the FEC. It recently formed an independent expenditure committee in Colorado, which may take unlimited contributions that must be disclosed. But if those contributions come from the parent group, it makes the money more difficult to trace. The group must first report its contributions to the Colorado Secretary of State on Sept. 1.

Then there’s Fair Share Action, which has purchased $249,410 in ads criticizing Gardner and the Koch brothers, who are affiliated with dark money groups Americans for Prosperity, Freedom Partners and others. While Fair Share is a super PAC that reports to the FEC, so far its only contribution this election cycle is from the House Majority PAC. The group doesn’t have to report its contributions to the FEC until Oct. 15.

What to look for this week: The RGA is paying $51,000 to air six 30-second spots during Thursday’s final Denver Broncos preseason game with the Dallas Cowboys, which airs on KTVD.

Here’s a graphic look at the ad buys so far: