A question on shadows

I was asked recently;

Stape;

I have a question on shadows and their color. I think mine are either too colorful, or too gray, or too.......something. They are very difficult for me, is there a guideline to follow?

I am very conscious of values so I think I got the light and dark stuff right, but those shadows are difficult.

CBH

Dear CBH;
let me load more bullets into the magazine, and here we go.

• Your shadows should always be darker than your lights. However in this picture I have cheated them really high key on the road. They are influenced by the material on which they fall.
• Outside they will tend to be cool. The warmer the lights the more this will be.
  
• I throw accents into my shadows to make them lively, see those in the ruts of the road?
• Notice how I use the weeds to interlace the lights and the shadows. Here is a link to a post about that.
• Remember that step one is observation. You need to be able to correctly observe what is before you and represent it. However, that may not be the best presentation. Sometimes you will need to be able to make some changes to get it to look better. The trick is to know when and how. There is one of the reasons that art is hard.
• In this painting I have cheated the lights towards a yellow, the color of the light, and painted the shadows the local color rather than as violet as they actually appeared.
• I don't know of a colored versus grave rule for color. I have painted them many ways and you have to figure that out for each picture.
  
• You will need to study both nature and the work of artists who came before you. There are answers in both places and neither can be ignored.
• Study Seago, Metcalf, Carlson, Constable, Inness, and Corot, these artists really knew how to handle shadows well.