As much as I like the color of water color pens, they are still wet when you’re using them. They don’t dry quickly and this can lead to smudges – from ink that gets on your hands while you’re coloring, or from ink that gets on whatever surface you’re coloring on.
Here’s what I’ve learned works for me: I use a clean sheet of paper when I’m coloring. If I leave the pattern in the coloring book, then I use two sheets, one on each side of the design. If I remove the pattern piece from the book, then I use one sheet under my coloring, then I rest my hand on the other one so that I don’t accidentally transfer color with the heel of my hand.
The only thing you want to be careful of, is if you have a particularly wet pen, you don’t want it to transfer from your blotter sheet to the design.