individual images as navigation design TwentyTen

You can change the black bar of header navigation of WP TwentyTen theme by changing the background property of access id but when changing it try to make new rule more specific as following :

body #access{           
       background: none; // Add here image or color whatever you want

To apply individual background images behind each link, add background property to #access li element as shown below :

body #access li{           
       background: url('image.jpg') no-repeat;; // Add here appropriate image path