Lol, it's interesting to hear a non-American perspective on this! Blue is the color of the Democrats (liberal) and red is the Republicans (conservative). I was looking at a map of the French presidential election recently, and was so confused because I assumed red is conservative & blue is liberal there, too.
As to your real question, to my ear, Jackson has a more "country" sound. It goes along with other surname style names like Landon, Logan, etc. that are newer as fns. Conservative states ironically tend to use newer names. The main exception to this is the South, which is conservative, but which has used surnames as fns forever...which is why Jackson sounds like a country name (it is also the last name of Stonewall Jackson, a Confederate general after whom many Southern boys were once named).
Jack, on the other hand, fits in with more blue state trends. It is more of a classic fn, so it goes with names like Nicholas, Joseph, etc. which I believe are more popular in blue states.
Oh, and the reason you'll rarely see little boys named Ronald is because it's very old fashioned as a name. It was hugely popular back in the 30s and 40s, so it's definitely still a grandpa name. The sound (with the double consonant ending) is also quite outdated. Reagan, on the other hand, fits in with a bunch of current trends: surname, ends in N, 'ay' sound... Add all that to the popularity of the president (among conservatives, lol), and I bet you have a red state hit.