As the sky turns toward dusk, purple flashes one more bolt of blue before night. Night Fall Thinking Putty changes from violet to blue with just the heat of your hands. As part of the Hypercolor® Collection this color changing Thinking Putty® is heat sensitive, meaning it starts one color and changes to another through heat transfer. The more you play the more the color will change! Thinking Putty® helps build hand and finger strength through a fabulous tactile play experience with unique, unexpected properties and provides relaxing, yet stimulating interaction for anyone with sensory integration issues. Crazy Aaron's putty is non-toxic, won't dry out, and won't leave a sticky or slippery residue on your fingers, so it's great for stretching, molding, bouncing, tearing, popping and playing by kids and adults alike.