The video above shows how plasma screen TVs function and how they are produced. The PLATO plasma displays were much simpler than this, being able to display only a single color (instead of 1 million), but the underlying technology is the same. Below you can see a PLATO V terminal showing the distinctive and highly visible orange glow.
If you want a more technical explanation for how plasma display work, check out this excellent article.
Finally, here is a video of Donald Bitzer himself discussing the creation of the plasma display.
(vid from youtube originally from a Discovery Channel show, image from wikipedia)