Lens Flare for sure. Remember you lens can act like a prism and have different color shifts throughout the rainbow. Also there is anti-glare coating on the lens to reduce this, but you can still get multi-color flares. You might have hand a finger print on the lens that helped cause the size and color.

Otherwise, I'd submit your video to the Ghost Busters and have them come remove the ghosts from your house. ASAP!

That's what worries me - I don't. I cannot for the life of me spot any weird blemmishes on the lens.

So it's safe to say that nothing is wrong with the sensor?

And that there may be some unidentified blemish somewhere on the lens?

I'd just clean your lens and learn not to let flares / light get on the lens. A clamp on french flag on top of the hand rail can flag any problem. If you are shooting into the light like a sunset, then you need to watch and adjust you camera - center the sunset - until it does not flare. Flaring is natural - now if you get this horrible look shooting something for real, then it shows you are not protecting you lens with a mattebox and or flags.

I'd go shoot a bunch of tests and see if you this happens.. screwing around you can get lots of stuff to look bad.. which is what your test shot was... dark underlit couch with crapping backlight flaring the camera in different colors... no control and you get uncontrolled outcome. Good luck. Shoot serious tests.

As a side, I was sloppy shooting serious tests, and had the sun hit my lens and like many other discovered with shallow near focus - lots of spots and dust inside the lens. The solution, do not have focus close to the lens. Shoot f.4-f5.6 with focus at least 5ft away from camera. Shooting f.20 with focus 0 to infiniti will reveal spots especially when the sun is on the lens. Shoot in the sweet spot and problems are less.

John,

It is simply lens flare, just go out into a real world shooting situation and shoot some footage. If the flare is on all your shots then you have a problem, if not then put your time to creative use.