In a bit of a rush so I won't quote people directly to save time. Apologies in advance if this post ends up being difficult to follow!So far pretty much every Pureblood that we've seen has boasted either white, blond or silver hair. Eye colour is more varied - with variants of blue being more common with the occasional example of green and yellow.
It's possible that we'll see even more examples of variations moving forward so I'd be very cautious about settling on any head canon just yet. With that said, though, the lore book did end up confirming a lot of my own head canon in regards to their culture and background.
As far as the criticism and claims regarding their supposed need to 'compensate' I strongly disagree. They were pushed around and forced to migrate into a hostile, barely hospitable environment and over time they made it their own. Despite being few in number they - with the help of magitek - struck back and proved that they were a force to be reckoned with.
When one considers all the strife that has arose from Eikons/Primals their stance on religion makes quite a bit of sense. In addition, it also makes sense when you consider that Ishgard exploited religion to justify their war against Nidhogg and his kind.
Garleans being revealed to have some capacity for magic - albeit as a rare affair - doesn't strike me as something that would be an oversight. To me it seems like it's something intentional that will play into the story moving forward. This might explain why Lucia casts 'Cure' on the Steps of Faith and also why Regula was able to teleport out of harm's way on two occasions.
Personally I'm hoping that at some point it'll serve as the means to introduce Pureblood Garleans as a potential playable race at some point in the future. If they ever go through with the plan to expand the character creation system and add more distinct 'Clans' for each race then 'Garleans' would be well suited to an additional type of Hyur.
Granted I may be repeating stuff that has already been put forward but the above is my rambling for today.