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DENVER — New numbers from OnSight Public Affairs and pollster Chris Keating show President Barack Obama leading Mitt Romney 48-45 percent in a survey of 502 likely Colorado voters.

It’s the second poll Thursday from a Democrat-leaning outlet showing Obama ahead of Romney by three points in Colorado, one of seven swing states set to determine the race for the White House.

Obama’s lead is driven by a 52-38 percent advantage with unaffiliated voters, the state’s largest voting bloc.

“In Colorado, it always comes down to who can appeal to the unaffiliated voters,” said Keating. “They are now the largest voting block in the state and the candidate who wins them over is almost certain to take the state.”

Keating’s survey, conducted with live interviews Tuesday and Wednesday as both candidates were stumping in the state, also has Obama leading by 10 points in the Colorado’s two most important swing counties, Arapahoe and Jefferson; and he continues to hold a significant, 52-41 percent advantage among women.

The President also holds a nearly 4-to-1 advantage among Hispanic voters.

Romney, meanwhile, leads by 10 points with men, 52-42 percent.

While the three point overall lead for Obama mirrors that in the Project New America poll of Colorado voters released earlier Thursday, Keating’s poll uses a somewhat different sample.

Whereas PNA’s survey sample included 34 percent Democrats, 33 percent Republicans and 30 percent unaffiliated voters, Keating assumes that the Obama turnout model is less effective at getting unaffiliated voters to cast ballots.

His sample breaks down like this: 36 percent are Republicans, 33 percent are Democrats and 30 percent are unaffiliated voters.

UPDATE: And another poll from NBC News and the Wall Street Journal released late Thursday afternoon has Obama and Romney tied at 48 percent apiece in Colorado.

It’s a five-point swing in Romney’s favor since the group’s last poll a month ago, prior to the first presidential debate.

“In Colorado, Obama is not hitting his mark with white voters, and is now losing suburban Denver voters as well as independents to Romney, who has also closed the gender gap versus the president,” NBC writes. “Enthusiasm among young voters has also fallen off for the president.

“Men and women alike in Denver’s suburbs have shifted toward Romney; a month ago, Obama led by 18 points among Denver suburban women, an advantage that closed to 3 percent in the most recent poll. Romney has expanded his lead among Denver’s suburban men from 6 points last month to 13 points in this week’s poll.”