The pressman running the press had the yellow too saturated on the run causing the yellow to be brighter not only in the yellow but in all the colors which all have yellow in them to a certain degree. Notice the hat intensity and the more orange red shade of the bottom bar. His flesh tone is also has more of a yellow tone. During the run the pages are compared to a prepress proof that has been signed by the client to manage color accuracy. The pressman's job is too match that on press by adjusting the four colors on press of cyan, yellow, magenta and black. The slightest move on press of any one color can throw the entire page out of whack and it happens all the time. The pressmen pull sheets randomly along the print run to make sure the colors are consistent. If it's not they adjust that color on the press controls. It always varies though. I've done hundreds of press checks over the last thirty years. It's really interesting to watch the process and how complicated it really is. Very different now with so many digital printing processes.