Working from a duplicate layer underneath, rotate and position
rectangular selections over each black line and some surrounding color.
Then copy/paste into a new layer, and reposition.
As long as you don't rotate the selection after pasting,
the angle is set correctly.
Fill in color with Paintbrush.
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Works pretty well for a background like this.
http://img80.imageshack.us/img80/7907/screenshot792.png