The “colors of the Jedi” seems pretty interesting! Also it would be less distracting that having the actual Force ghosts appear (though I kind of wished for that to happen as well).

I also onboard with Green Mist Exegol. A couple of days ago I revisited the Son of Dathomir story (in audio-comic form) and remembered that Sidious used to exchange knowledge with the Nightsisters of Dathomir. That, and the fact that the witch Talzin’s resurrection very much parallels Sidious’ comeback (to the point both characters drain a powerful Force-user’s life force to restore their physical shapes). The greenish tint to Exegol could serve both to make the planet more interesting to look at, and serve as a fun Easter Egg (connecting it to the green-mist appearance of the Nightsister spells) that hints to the “unnatural dark side abilities” Sidious could have used to return.