A lot of the illustrations in the books are doodles (unplanned drawings) that I've done throughout the years... but, also, there are illustrations that were done just for the books. I think TOMBO pens work best for coloring them. One tip is similar to a brush... and the other is a small point. Also... Prismacolor pencils work pretty good on the images that don't have crosshatching on them. There's some samples on this Facebook group page... https://www.facebook.com/media/set/?set=oa.351071395224088&type=3 . And if you'd like to see some of the other kinds of art I've done, I have a group page on Facebook called THE PRESTON (Like my stuff?) PAGE, https://www.facebook.com/groups/106859739347010/