I use GIMP and MS Paint to edit my chararts. There are a few important tools that I use.
The small hand is the blurring tool. I use that to blur the shading or markings that I put on the charart.
And on the tool bar below the spray tool is selected. I use that to add shading and highlights.
I use the fuzzy circle brushes to add the shading.
Use this guide to know how to colour in the eyes on your charart
This chart will help you to decide which ear pink colour will be best for your charart.
This is how the shading should be on the various blanks.