In a former life I did atmospheric research, flying in and out of thunderstorms, and saw a lot of interesting electrical activity around the aircraft, and in the aircraft.
What you're describing sounds similar to something I experienced about fifteen years ago in an area where there was considerable airborne dust, but no convective activity. I became aware of a soft blue glow from several points outside the cockpit, which became brighter until they formed what looked somewhat like those dancing tube guys that you see at car dealerships, waving in a flickering pattern ahead of the aircraft; at that point they were a greenish glow that had a simliar hue and appearance to the Aurora, a little like dancing flames extending off in three radials, or lobes. They gradually merged from the radome area, extending forward, in what seemed to be about twenty five or thirty feet ahead; I can't really say because it would have been hard to give a definitive answer. Somewhere out ahead. At that point, the one lobe was about the circumference of the radome, and increasing in intensity toward a yellowish hue. I was on the edge of my seat, fascinated, as I'd never seen anything like it.
A loud crack or report sounded, which accompanied a blinding white flash, like a lightning strike. In lightning, turn the cockpit lights bright. I'd turned everything down so I could get a better view. I was unable to see my hand in front of my face. I asked my compadre if he saw it, and he mumbled "uh-huh." I noted I was blind, and asked if he could see. He mumbled, "nope." Our vision returned shortly after that, and we joined an approach and landed. The event occurred at night. On the ground, I found holes and burn marks all over the radome, fuselage, wingtips, and numerous other places. Ultimately, the engines were removed, the airplane and engines degaussed, and the aircraft returned to service.
I was given some heat about allowing a lightning strike and accused of putting the airplane in the position to be struck, in a thunder cell. In that case, there was no cell anywhere in the area, nor did anything show on radar leading up to the event, which I'd describe as a massive discharge. No further signs were obvious, or occurred after the discharge. I strongly suspected the higher dust content where we were flying, helped contribute.
Some time later I had a conversation with someone in the maintenance about the event. "Didn't anyone tell you?" he asked. The aircraft had been painted, and bonding straps and discharge wicks placed over the paint, with no electrical bond. The paint was never removed from the bonding sites, meaning that the aircraft built a charge that it couldn't dissipate, until the charge finally passed through control hinge points, engines, etc, causing considerable damage. The flight control hinges were burned.
I can't speculate as to why you saw what you did, but there are numerous manifestations of electrical charge around aircraft, which range from the familiar corona or St. Elmo's dancing around or flickering, to discharges around the structure, buildup of a glow or corona around various components such as radomes, engine inlets, propellers, etc, to discharges which can occur within the cabin, or visible manifestation of electrical arcing or progress through the interior.
So far as those. yellow and green returns go; be aware that some of the worst I've experienced in a thunderstorm wasn't in the red and magenta parts, though we flew back and forth through some massive cells; the worst I ever experienced was in the black and green on the upshear, or building side of a cell, and it was rising moist air from beneath the aricraft (we estimated 12,000 fpm rising), which rolled me inverted, caused a shaker and then a pusher activation, and broke things on board, including my headset, and a computer chassis in a case...stripped a drive right out of the chassis. We're all aware of radar shadows, where returns can obscure what is beyond through attenuation, but there's bad stuff above and below, depending on where you are. Don't forget use of your tilt, and remember that even in returns that look not-so-bad like simple Level 1-2 returns, it may herald something that far exceeds the capability of the aircraft to respond. Been there. Don't you go there. Have an out, and always consider a divert, if needed. Extra fuel is a good thing.