They did describe the 'obsidian' crystals and wine to be purple-colored, huh? Come to think of it, I now wonder what the prerequisites/conditions are to make Asterion's spilled blood to remain as a liquid rather than harden. Asterion has been bled out in the dark room for decades after all. The only instance when this did happen and mentioned was in the past when Laomedon trained with him. Even in the much recent goring of Asterion in the ruthless route, it wasn't shown (and he only bled red in his sprites?).