Quoted from jrpinball:
"Sing Along" and "Melody" have four pairs of carolers depicted on the backglass, each dressed in colors corresponding to the four groups of four colors that you try to complete when playing the game.
Curious (since I own a Sing Along) - I've noted the four colors of the carolers, but it doesn't seem like they light up with any particular activity on the playfield. Are they supposed to? I do have flashers in the "Music" sign.
On my Flip A Card, I have flashers on the name that lights @ game over. In my opinion, this is one of the most attractive flashing elements on any EM. The green of the letters really pops against the purple and looks great.