The results of each presidential election, and thus the determination of which states went "red" verses those that went "blue," change in each election. Following each presidential election, news outlets such as CBS publish maps showing whether a state's votes went to the Republicans ("red") or to the Democrats ("blue").
In the 2012 presidential election, President Barack Obama won re-election over his Republican challenger, former Governor Mitt Romney. In doing so, Obama won 26 states, in addition to the District of Columbia, while Romney won 24 states. In 2008, when Obama first won election, he won 28 states plus D.C., while Republican John McCain won just 22 states. In 2012, Obama failed to carry the votes of two states he won in 2008, Indiana and North Carolina. Therefore, maps published after each election would have had a different set of states mapped as red and blue.