Sorry about the lack of descriptive title, but not honestly sure how to discribe it.
Anyway, given the background effect on this picture (and many more like it): http://www.iphoneclub.nl/wp-content/uploads/2008/09/image0013.jpg
How do i do this? I'm talking about the white lines which cover a simple background colour.
I'm sure this is simple but i can't work it out.