My son is crazy about two things: cars and water. So I was thrilled when I found the Humvee color shifter at Target recently. I explained to him how it worked - warm water would make it yellow, cold water would make it dark blue.
Well, the warm water did turn it yellow, but cold water doesn't do a thing. It would not change back, leading to tears of frustration on my son's part. I ended up putting it into the freezer, where it turned green, not blue (it's supposed to turn the color of the stickers, thus camouflaging the stickers to become a regular humvee rather than a rescue truck).
Though the packaging says it will hold the color at room temperature, it started turning yellow as soon as it was out of the freezer. Now it's sort of got a blotchy green/yellow thing going on. Its only saving grace is that it's a car and can be pushed around like all his other Hotwheels and Matchboxes. Definitely not worth more than the $1 a regular car costs.