system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why in old films of NASA and USSR rocket launches do the NASA engines emit yellow flames and USSR 's are blue?

>I've been watching "Chasing The Moon" on PBS and in the historical films of NASA launches the US vehicle engines pour out a very yellow, smokey and less structured flame than films of Soviet rockets where there's very little smoke and the flames look almost like what you would see on a gas stove. Blue and a very tight flame.  Is it the fuel? Basic design?  Maybe the color rendition of film itself?
gpt
It could be the fuel as almost all US rockets use liquid oxygen + kerosene which results in yellow glowing exhaust due to all the carbon left in it. Though the most used Russian launch vehicles were/are from the R-7 family that use the same fuel and generally their exhaust looks the same, Russian Proton rockets use nitrogen tetroxide + hydrazine which does burn in a more clear flame.