After a quick search on YouTube I was somewhat unsatisfied; the few videos I looked at showed the effect only partially. People do sometimes like to bias the burn towards the yellow flame, either for entertainment or to keep the temperature of the stove down. Also it's hard to capture. My own attempts to photograph the effect haven't been successful due to the movement of the flame and the gentle low red glow that it gives off.

I've never seen it before (so I'm not 100% this is the same thing), but did find a picture that I think is similar to what they're describing - the red glow in the top window of the picture here: https://commonsensehome.com/masonry-heaters/