Why Rocket Exhausts Look The Way They Do

I have read and been told, a good engineer can tell a lot about how the rocket engine is running by just looking at the exhaust.
Scott Manley goes into some good detail on why rocket engine exhausts look the way they do.

Video Caption:¬†Why does the exhaust from the Space shuttle boosters & engines look completely different? There’s a huge variety in the appearance of rocket exhausts because different fuels, different technologies and different environments make them behave in a different manner.