It would be VERY helpful to know where this particular snake was seen. In the eastern US, Corn snakes sort of match that description, and so do hypomelanistic Midland Water snakes, though neither of them has diamond-shaped markings. Actually, very FEW snake have diamond-shaped markings, but I've noticed that many people tend to all ANY pattern they see on a snake a "diamond" shape. Corn Snakes have rectangular blotches on a red-orange, yellow, gray or orange background.