That photo does not look to me like a stock color for a Chevy AD truck that a code would be available for.
If it happens to be a stock color for any manufacturer or year, go to paintref.com
Link and take your pick of whatever looks closest. Then take that code to your paint supplier and have him mix it up for you.
Or you could print the picture out and take it to the paint supplier and have them match it from the photo. Be advised that it may look totally different because of variations in colors on computer screens and printers.
