Dark, Medium, and Light
Everything you look at is made up of values. Values are the shades of color that give shape, body, and depth. Even the brightest object like the sun has values. When you first look at it is round circle of orange or yellow. When the sun is setting on the horizon line it is really much more than that . The sun has a very bright spot but the rest of it is broken down into shades. There are very deep spots of color and medium shaped. The gradient of color is what makes the run look round.
As you go to translate this on to paper or canvas, it is important to remember that there are very dark sections of an object as well as extreme light areas. It is not all one color. Defined areas of dark, medium, and light will create the shape and depth the capture the essence of the object.