I love coloring parts of my pages in. Oh, how it brings me back, calms me down and makes me focus on the present moment. I used Glaze and Souffle pens to color in the circle design. I try to let each color dry before I start the next layer. If you're using a Rapidosketch to outline any work done with a Glaze or Souffle pen, make sure that pen work is dry before you use your fine tip Rapidosketch. I also like to have scratch paper nearby in case my markers and pens start to misbehave. Usually a quick mark made on scrap paper seems to help move the ink along.
More tips on Glaze and Souffle pens here.