When the mug is cold, the mug shows an image of frog outlines. Add a hot beverage to see bright colors of eleven different species of poison dart frogs. A great conversation starter and must for frog lovers! Wonder mugs are color-changing coffee mugs that change dramatically when a hot beverage is added. If you're looking for a unique gift for them, what a unique way to remind them of you daily! These unique, high quality gift mugs utilize color-changing or “thermochromatic” ink that changes color when hot beverages are poured into the inside of the mug. Color change gift mugs are ideal for fund raisers, birthday gifts, teacher's gifts, corporate gifts and more. All Wondermugs are microwavable. We recommend hand wash only (no soaking) to preserve the ink.