Thanks a lot...
In fact the gradient colors are from a simple gradient bar (black to white) added to the general color, in another layer (-> "Edit Style" panel).
You can use a gradient from dark grey to light grey if you don't want too much contrast between the colors.
And the larger the white is the more you will have a thicker "light" line. The larger the black is the thicker the "shadow" will be. (Hope you can understand my bad english !?!)
As you can see here I have replaced the white color by a grey color to reduce the light effect at the top left !
I have added outlines to create a background like in Comic books.
Edited by p6r, 22 September 2014 - 11:16 PM.