Hope you don't mind the double post/bump. I intended to add Galaxy/Comet to the list but I know that's a scheme that merits its own thread for a full color scheme breakdown.
And what a mess of a breakdown it is!
TL;DR version:
1. There are about 5 main colors within the Galaxy/Comet.
Galaxy Pink (#e6a2ef), Galaxy Purple (#b36adb), Tanzanite (#5159d9), Lapis Blue (#314bf4), and Azure Blue (#1accf4).
Galaxy Purple appears to vary the most with exact hue and brightness, but it's difficult to tell what's a part of the ombre and what's not, so I grabbed the closest and most consistent hue.
2. The main distinction between 'Old Galaxy' (Galaxy Pink and Tanzanite, with the occasional Plum) and 'Old Comet' (Jet/Black, Azure Blue, Galaxy Pink) from their modern versions are the presence of Galaxy Pink. Modern recolors rarely use Galaxy Pink anymore, and are more inclined towards Galaxy Purple, and Azure and Lapis Blue.
3. For certain color combinations, Gaia makes no distinction between Comet and Galaxy, or at the very least, does not consistently tag either scheme.
Comet is consistently Galaxy Pink, Azure Blue, and either Tanzanite or Lapis Blue. However, exchanging Galaxy Pink for Purple makes it a toss-up. Cosmic Diamond of the First Water and Cosmic Rabbitually Late are both tagged 'Comet' but Galaxy Sky Terrarium and Twilight Sleeping Willow are not, despite both using the exact same colors.
Ultimately I think it's pointless for the distinction to be made (in reference to the G. Purple/Azure/Lapis combination), at least until Gaia has made up its mind about the scheme.