Stampin’ Up! has lots of videos about coloring. Here are a few.
Coloring on Vellum
Watercoloring with Blender Pens
Watercolor Wash
Watercoloring with Stamps and a Stampin’ Spritzer
Watercolor Background with a Clear Block
Dip-Dye and Faux Dip-Dye
Stampin’ Spritzer
Spritzing and Splattering
Coloring with Stampin’ Write Markers
AquaPainter vs. Blender Pens
Kissing Technique
Stamping with Embossing Folders