The blue one is a color changeling, with the red and yellow components of the inks bleached out either by sun or chemically. Note the red stripe on the pants leg and the background "'47" is completely gone as is the yellow shoulder patch and flesh tones, among others.
Use the search function to find other examples of changelings.
Used stamps are always extremely suspect when it comes to missing colors. As my Mom always used to say, "You don't know where that's been." Mint stamps at least tend to get stored out of sunlight and away from chemicals.
The blue here is actually cyan, one of the colors used in process printing where little dots of 4 colors (cyan, magenta, yellow, black) are used in combination to create all the colors you see. Equal amounts of magenta + yellow makes fire engine red. Modern printing presses have at least 5 colors (with a greyish black for tones and full black for lettering and such). This is all done in one pass through the press, so that missing colors are very rare today, as NSK said.