Aside from Charmed, McMahon is known for his starring roles in Nip/Tuck, FBI: Most Wanted and the 2000s Fantastic Four movies. He died July 2 in Clearwater, Fla. from a private battle with cancer.

Sure, some holiday color pairings are obvious—red, white and blue for the Fourth of July, or green for St. Patrick’s Day. But Halloween’s iconic shades feel a little more mysterious. Is it just about ...