So here's the answer - keep in mind it is a Pilot's Cross, not a passenger's cross.
Consequently it is seen only from the cockpit, not the side window. Which let's out the easily googleable passenger window video.
Yes,it is a "glory", ie a circular rainbow. When approaching a vertical cloud surface, typically a tall cumulo-nimbus in the afternoon with the sun behind you, you see your shadow on the vertical cloud face in front of you. It starts out with the rainbow large and the shadow small. As you get closer, the shadow gets bigger and more distinct, and the radius of the rainbow gets smaller. Keep in mind this happens at upwards of 200mph. At about 1/2 second before entering the cloud, the rainbow is bright and has shrunk to the size of your shadow, and the cross formed by the wings and the aircraft vertical stabilizer fill the circle. Your wing shadow rushes through and past the circle; faster than you can process it the cross grows large and the rainbow shrinks to a point. That is the Pilot's Cross. And in the wink of an eye it is gone, you fly right into and through the movie screen cloudwall, and you are from the bright into the murk.
I've tried capturing the moment, but the camera is always fooled by the bright sky and does not see it as our eye does. It gets very washed out.
"It's Irish luck and Dorothy,
Reflected refractivity.
From bended bows when all is right,
The Pliot's Cross comes in to sight..."