Did a couple of searches online, no results. Tons of them without any flame whatsoever, and the pics I've seen and brief video clip in a documentary were on takeoff so I presume it's only when the engine is at full power (i.e. takeoff?) that you'd see them. The photo and film were very dark and you only saw the flame against the darkened plane behind it as it as moving away from you. Chances are it wasn't so obvious to the naked eye but possibly still visible.
Don't have a scanner but I've got a small pic of an Ar234 with flames in one of the (few) books I own.