Not he. No one really knows. But anyway, Spencer, that's because he/she/it chooses to add renders that fit the colour and then adds an overlay style to them. Fits nice.
Anyway. Julaman... how ever you spell it. I was terrible when I started. Playing about with Photoshop is one good thing to do, but I recommend using tutorials first.
www.pixel2life.com is very good for this kind of thing. They have an area devoted to sig creation.