Oh... water-based won't stick to walls. But at least the pigment used in both is the same.

[Then again, all she knows are that fresco and oil paints are the only kind that will stick to a wall's surface... at least, they were the only kind in her time. Thus, she's assuming he means watercolor, which is fine and dandy, but not exactly what she's looking for.]

The sparkly paint sounds really neat, though!