Yes, Colorado is a blue state.
As of this April, voters who affliate as Democrats now outnumber those who affliate as Republicans in Colorado. This follows an eight year reversal of control in electoral politics. Political identity as show in voter registration is a lagging indicator of actual voting practice. This also reflects a grass roots orientation in Obama's Presidential campaign not shared by the McCain campaign, and the impact of a long contested Democratic party primary that kept the Dems organized and involved to a greater extent.
Of course, a large share of Colorado voters remain unaffiliated, at least publicly, although Democrats have been getting a larger share of the independent vote than Republicans in recent years.