Hue and color are the same thing. But the gray scale tells you how deep or light your color is.
Every painting has multiple planes, a minimum of 4 or 5. A landscape can easily have 6-8 planes. A basic rule of thumb is everything on the same plane should have about the same value for the main components. Each component also needs different values to give it form. That should be about 2 value shifts. With a gray scale and value finder like mine, I can put it over the dominant color in a particular plane and find out what value it is. Then I can look at other colors in that same plane and see if they are more than one or two values off. If they are, you probably need to adjust that hue or it may make your painting look off.
If your painting looks flat you can almost guarantee that your values are off. Usually it means there isn’t enough value shift in a particular subject so you can’t really see the form of the subject. If a vase, flower, animal, etc looks flat, it’s almost always there isn’t enough difference in the values either in the item or the shadow.
Understanding values is a bit time consuming and can be frustrating but it is absolutely one of the most important pieces of the puzzle in improving your art.
