Coloring books are not making the top 10 bestseller list on Amazon because kids are fueling the craze. The hottest coloring books right now are the ones designed for grown-ups, and adults are buying them as their own preferred playtime activity workbook of choice. Neat? You betcha! Now it's time to look for your favorite set of color pencils, color sharpies or just good ole plain crayons to get you started.