It's just another media invented term.
I've always wondered why when the US military do wargame simulations, the blues are freindly forces, the enemy are red. I also wonder why the liberals are so much more aligned toward socialism and communism, shouldn't the Democrats be the red states.
To answer your real question, there is no such thing as red/blue states. There are many people in all states that vote opposite of their neighboring citiy or county. Unfortunately, I live in California. I know my vote doesn't count, but I still always vote conservative. People in a 'blue' state aren't all blue, and vis-a-versa.