[Solarwater]

So... I'm working for an engineering firm this summer and my boss wanted me to find a substance that makes a transition from colored to clear in water when heated to 110 degrees fahrenheit. My first search provided me with water soluble thermochromic microcapsules, which can be made to change color at a range of temperatures, my thought being, dissolve the powder in water, heat the water, and watch it go clear. However, once cooled, the substance reverts to it's original color. My boss wants something that, when heated to 110 degrees, dissolves into the water becoming clear, and stays clear after the water is cooled. Now, it's been a while since my chemistry class, but if something dissolves at 110 degrees and is cooled, doesn't the water become supersaturated? And if so, won't the substance un-dissolve if disturbed (forgive my lack of proper terminology), returning to it's original color? Or is there a substance that doesn't follow these rules, and stays clear once dissolving (into water) no matter what?

[Solarwater]

If there is such a substance, could someone tell me if it is toxic or not? Or are thermochromics the only solution?