This is cool. Just some nerd fun.
Check out the first video. This shows a launch of the Russian Soyuz space launch vehicle, the old workhorse of the Soviet and Russian space programme. It’s lineage goes all the way back to the R7 Semyorka, the first Soviet ICBM and the booster that hurled Sputnik into space.
Notice the black soot? That’s because the Soyuz uses Kerosene as a propellant in the core booster.
Now look at the launch of the Hwasong-14 on July 4. Notice the translucent plume, and no soot. That’s because it likely uses UDMH, unsymmetrical dimethalhydrazine, as proplleant fuel which is a colourless liquid. In contact with air UDMH goes yellowish-orangey. UDMH became the propellant used by the Soviet Union’s more advanced long range liquid fuelled missiles (the Semeyorka wasn’t really a viable ICBM).
The development of a high thrust engine fuelled by, most likely, UDMH propellant is a key advance in North Korea’s strategic nuclear programme.
Here’s a launch of the Soviet/Russian SS-19 liquid fuelled ICBM. It is fuelled by UDMH propellant.
It could well be the case that the Hwasong-14 tested on July 28 had a higher combustion chamber pressure in the booster engine than the July 4 Hwasong-14 test, which would equate to greater thrust.