Blue lava rock, like the unusual "Blue Dragon" lava, gets its blue color from the way light interacts with tiny mineral crystals within its glassy outer layer. Specifically, intense blue light is reflected from clusters of minuscule titanian magnetite crystals that are dispersed, along with crystallites of plagioclase and olivine, throughout this clear, brown glass layer.
In essence, it's the optical effect caused by the arrangement and composition of these microscopic crystals that gives the rock its blue appearance. This is different from the actual color of the molten lava itself, which is typically red, orange, or yellow.
