For Skysail, White and Green are represented by their sense of community and peacefulness, while the Black is likely manifesting through their desire for independence, again pretty opposite to the Abzan.
I don't want to keep on going on and on about this, but "desire for independence" reads like a red thing to me. It's not like black can't have it, but it would have to be associated with a somewhat predatory material/political/societal gain. Maybe it's just me, but I can see a "independence to ensure peace and the security of the community" mindset as Naya, Jeskai, or Mardu - definitely not Abzan though, especially when black is supposed to be the center color.
Looking through the spoiler again and finding things like Facet Reader, I got the feeling that the human settlements on Ikoria are simply less defined by their colors than the Tarkir clans. At first I thought "settlement X is mainly [wedge] because it's in that region" was a weak argument, but it might just be this way. Drannith definitely is the settlement that best matches its colors in terms of philosophy, with Lavabrink coming in second and Skysail third.
The Skysail is floating for safety's sake, not necessarily because of freedom (a side benefit perhaps). Valuing safety via congregation is a W/G trait, soaring above the danger (B) below them. Though, there's no deny that Skysail could go else where when they choose to, as we saw in Xyris, the Writhing Storm, but the "Jeskai" region of Ikoria is Raugrin, that place is filled with flying dinosaurs so Skysail's advantage is naught over there. Indatha is terrible but most threats appear to be nonflying. Most.
Hm, I'm not convinced.
First off, if "safety via congregation = GW", then Drannith should be G as well.
Second, interpreting B as "the danger below" seems very flimsy, especially since monsters of all colors are dangerous and black is supposed to be the central color of the wedge in this case.
I'm pretty sure a group that is mainly B and has GW as its secondary colors would laugh at the idea of Skysail. Abzan is one of the most pragmatic color pairs, it favors conservatism and "playing it safe". You need a lot of idealism to propose something like a flying balloon city, let alone actually build and run it. BGW would see something like that as a waste of time and resources at best and suicide at worst.
Also, all cards that picture Skysail (or better, Skysail itself and its inhabitants) that we've seen so far have clearly lean towards Jeskai: Valiant Rescuer, Decoy Gambit, Fluctuator (in the Jeskai commander precon) and Twinning Staff (it's colorless, but if you had to apply colors to it, its effect would be RU). Additionally, blue and white are the main two colors for flying.
Quite a few cards picture balloons being destroyed so I'm not sure if there's really a region that's safer than the others, but yeah, maybe they moved over Indatha because it has the least number of airborne threats.
For the city they talk about being able to separate out into small groupers then come back together as a bigger whole which kinda feels white or white/green so that might be that aspect of it.
Skysail is mentioned in the Indatha section, but even going by the little information we have about it, it very much feels like a "Rwu" type of place. The main value is freedom (R) which is achieved by careful planning and engineering (U) and a strong social structure (W) which are both necessary to successfully maintain a floating city that has to defend itself against giant sky monsters.