To a lesser extent I'm curious about what color marble Xin-Eurythnia used.
I'm guessing white given Sorshen's seeming favorite colors (red and white) and how Thassilonian architecture was described. However, she built the Grand Mastaba out of black stone, and given Korvosa's fetish for black marble you'd think the color of the Gatefoot and Pillar Wall would've been mentioned if they stood out.
So I'm still confused.