There are many types of paints and plenty to choose from when tinting your embroidery. Watercolor paint is soft and beautiful. The color usually bleeds, so if you want a crisp line, create a stencil with freezer paper. The watercolor also makes a great background, rather than a fill, and can be used for landscapes, starscapes or more.
Start your coloring journey in small steps, think about block coloring using pen or pencil. This will give you the basic skills of applying color to the page and get you comfortable with the techniques to control your pen or pencils and stick within the lines.