The red states are those where the plurality of adherents are Evangelical Protestants; the blue states are home to a plurality of Catholics. Yellow are Mainline Protestants, while green states have "Other" as a plurality, which clearly means Mormon in the three states in question.The curious aspect of the map is that Jarman decided to ignore the data of "unclaimed" persons in each state. These are people who are either non-believers (welcome, my fellow godless Americans!) or are not associated with any "organized" religion. If he had included that data, the map would look very different, but he was trying to show the correlation between evangelical belief and partisanship.
However, if you look at the actual data yourself (which is publicly available), you can see that in most states the unclaimed dominate the population, with the Top 5 "unclaimed" states being Maine (72%), Oregon(69%), Vermont (66%), Alaska (66%), and Nevada (66%).
That's today's lesson in godlessness, folks!