What makes these six Roman emperors different?
My brother has a poster of the Roman emperors and the years they served in order from Augustus to Romulus Augustulus. The portraits of the emperors are from the coins at the time, with all but six of them being a metallic gold color. The other six are a metallic grey color.
My question is, what do Maximinus Thrax, Gordian I, Gordian II, Balbinus & Pupienus, and Honorius have in common that would require them to be differentiated from the other 67 emperors on the poster?
He got the poster about a decade ago in Germany. It has some text at the bottom that just explains which emperors they picked. It says only emperors who ruled independently by their own absolute power were picked. No co emperors like the sons of Marcus Aurelius. Once the rule of four started, they only picked the senior emperor for the Western Roman empire.