A head to head comparison of the Colorado 2012 General Election gives us an idea of the break down of the voters.    

Barack Obama received 1,238,490 (52%) votes, beating Mitt Romney who gained 1,125,390 (48%) by 113,100 votes in Colorado.

Mitt Romney won 37 counties whereas Barack Obama won 27 counties in the total of the 64 counties in the State of Colorado.

Presidential General Elections

During the 2012 General elections, over 122M total number of votes were cast. Barack Obama got 62,614,654 (62.6 Million) over Mitt Romney's 59,141,654 (59.1 Million). He won the popular vote by 3,472,979 (3.4 Million). His victory at the State of Colorado (with 1,238,490 votes) represents 1.9% of his popular vote victory. The remaining 49 states contributed to the remaining 98.1% popular votes victory.

Top 15 Counties in Primary Elections vs General Elections

All Candidates (General Elections)

These 15 counties play an important role in these Primary elections. If a candidate, can get a sizable majority in the larger counties (Jefferson, Denver, El Paso), it is still possible for other candidates to catch up, given the amount of large counties of similar size.

General Elections
Barack Obama

General Elections
Mitt Romney

Jefferson and Denver, two of the larger counties, voted in favor of Obama giving him a 153k vote advantage. El Paso, another larger county voted in favor of Romney giving him a 59k voter advantage in that county. However, Romney's steady win in the less dense counties wasn't enough to catch up, making Obama gain an upper hand in the State of Colorado.

Related References: 2016 Colorado Primary Election Story, 2016 Colorado General Election Story, 2020 Colorado Primary Election Story, 2020 Colorado General Election Story