I thought that adding eyes might take away from the symbolism and wouldn't really add anything special to the piece. Plus Kirie (the first girl) has hair covering her eyes, and Reika (the third) has hair covering one eye, and Sakuya (the fourth) has a distorted face so you can't see her eyes, haha.
Amazing concept! I never thought I would see these characters drawn into something like a stained glass window. The character-appropriate backgrounds are great, too, although I'm not sure how the yellow background on the left matches Kirie.
The characters themselves are quite striking. I love the positions of Kirie's multiple arms and the flames on Sakuya's kimono. Reika's chest doesn't look right to me, though. You have light blue alternating with dark blue/red for seemingly no reason, which doesn't look anything like Reika did in the games: [link]
AHHH I am so sorry this reply is going to be kind of lame; I had a huge explination typed up and then my computer refreshed the page and I lost it Dx
Anyway, the main reason I picked yellow for Kirie would be the lack of an obvious theme colour for the first game. As I was thinking back to it, brown seemed like a good choice as there was quite a lot of it (as well as grey), but when I played with shades of brown, it was kind of an ugly background colour for stained glass. So I kind of thought about which colours are close to brown and ended up picking a light yellow.
As for Reika, I will admit I kind of took more liberties with it than I should have. However, I do have a good reason! In game, it states the Engravers use two different kinds of ink to tattoo the Tattooed Priestess-- Red ink (from the blood of the living) and Indigio ink (from the blood of the dead). And when I looked at Reika's tattoos, I noticed that her tattoos were more of a royal blue than either red or indigo. So I kind of went with what the game says the ritual entails with rather than what Reika's physical character design looks like... especially since both Miku and Rei's tattoos include red as well as indigo (though Miku's includes significantly more red) c: