With two days of early voting in the books for Colorado, 325,000 votes have been cast. This makes up almost 10% of the active registered voters.
Republicans have a slight edge in voter registration overall in Colorado. Here are the early voting stats so far.
Of the ballots cast so far, 39% have been from Republicans, 37% from Democrats, and 27% from unaffiliated voters.
The breakdown on Oct 23, 2008 showed only 85,000 early votes being cast. Of those, 40% were Democrats, 33% Republicans and 27% unaffiliated.
I imagine that this gap will shrink over the next couple weeks and be what it was in 2008.