I have also read that, on night flights, long purple exhaust flames were visible, coming out of the engines, across the wings and saddle tanks, full of highly flammable Avgas! Perfectly safe, but I think some passengers would have needed some reassurance from the crew.
Here's Chesley Sullenberger & Jeff Skiles
checking out in a 7B rather than a 7C, but the flaming exhausts are spectacularly demonstrated.