Gel Pen Sets For Coloring – 5 GREAT Options! A lot of people are clamoring for gel pen sets for coloring these days, due to the ongoing popularity of adult coloring books. The first commercially successful coloring books came out in 2012 and 2013. By 2015, coloring books such as Enchanted Forest and Secret Garden had reached the top of the Amazon bestseller lists. This post, it’s photos and table include links … [Read more...] about Gel Pen Sets For Coloring – 5 GREAT Options!