Hey there @CycKlone! Welcome back to the forums!
So generally if we want to propagate changes to the system we’ve got two options. You can either set the color parameter via blueprints and bind that parameter to each of your systems, or if you’re really fancy you could work with creating a module that does it, however I’m not a fancy person so I’ll give you a quick run down of how I’d do this via BP.
So in your Niagara system, make a new parameter for Linear Color. I just named mine Linear color because I’m not very creative.
Then bind it to whatever color you want to be synced and do this for every single emitter you need.
then head on over to whatever actor BP can make a reference to your Niagara system, might be it who spawns it and can get a reference due to being a firework. Then you’ll make something a little like this where you either build a new color from code (where you can randomize it) or put in another color however you want.
and voila!
Hope this helps!