Until yesterday, Colorado had one superdelegate slot open. It was going to go to either Mayor John Hickenlooper or former Mayor Federico Pena. Yesterday, Mayor Hickenlooper, who has been neutral in the presidential campaign and intends to remain so, withdrew his name from consideration. Pena is an Obama supporter. The Mayor's explanation makes sense:

[He] said he is already credentialed for the convention Aug. 25-28 and that he would have plenty to do as the mayor of the host city. ...I've been focused on other things," he said. He also pointed out that he didn't seek out the at-large position but was instead nominated for it.

Mayor Hickenlooper's neutrality is important while the nomination process is ongoing. It's not going to come down to a fight on the floor of the convention, so his vote wouldn't make or break either candidate. This way, he keeps the good will of all of Denver's citizens, regardless of whom they have supported in the campaign.