The simple answer to this question, from Radio Flyer, is that red wagons always sell the very best. For some time, Radio Flyer made wagons that were blue, green, yellow, and colors of many kinds. But red has always remained the most popular to purchase, and eventually, through the natural desire of consumers, this color of wagon became an iconic piece that represents the American childhood. You can find multiple kids' books written about this question, explaining to children why their wagon is red.