When it comes to introducing young students to the basics of painting, many teachers use watercolor paints. They generally come in a rainbow of colors, and the student dips the brush into water and applies it to the solid paint color they choose. Once the brush has been loaded, they can then apply it to the paper. This is a water-based paint, and the pigment will adhere to either paper or canvas as the water evaporates.
Students who know little about painting can appreciate watercolors because they are transparent once applied, and the beginner can see exactly where they might need to add more paint. Unfortunately, once applied, they do not come off the paper or canvas. They do give the student the option to see where they might have made an error, and this is a plus when learning. It helps them with placing objects in the correct area of a project, and it further teaches them how to plan their projects.
Advanced artists also enjoy watercolor paints, and their translucence is the reason. Few artists who paint do so without first drawing a sketch on their canvas or paper. If they have abundant experience, they will generally only sketch broad strokes to give them the placement of large objects. They use this method to assist them in getting the dimensions of large objects correct, and detail is left up to their imagination when they begin painting.
There are some paintings that are designed to be less colorful, and paint is not necessary on the entire piece. Artists who create detailed sketches may prefer to simply highlight a few areas with color to focus attention on them. This is one method experienced artists have used for years to create just the right amount of color to enhance a sketch without covering it up.