I guess the first question it makes me ask is “why is this the first time the colour has changed?”
Palpatine has always been all the Sith, based on how things were presented and how Return of the Jedi was recontextualised.
Any time something changes it’s nature or look, there needs to be a reason why. If Palpatine is being restored, that would take him back to where he was in prior films. If it makes him different from that, it’s a question as to why.
Saying “it’s a new colour, that means new power!”… well, exactly. That new power isn’t explained, and we already have a lot of new powers and power levels that have gone unexplained. If you were gonna go back and recolour all the lightning in AOTC, ROTS, & ROTJ to match, then I’d be on board. But just in this one film seems silly.
Palpatine and Vader can both use red force lightning, I didn’t just randomly suggest it for the sake of referencing Mortis. We just haven’t seen it used in live action yet, outside of clone wars and comics.