Click on the image to view full size
Then click on one of the coloured squares
(mousing over it will tell you whether it's foreground or background).
Once you have a colour you want, click OK
at the bottom.
Then when you paint with the paintbrush
or use the bucket fill tool, this will be the colour you use.
Layers > Promote Background Layer
Effects >Art Media Effects > Brush Strokes
Effects >Texture Effects > Fir
I also suggest as a last step, applying Effects > Image Effects > Seamless Tiling as this
will allow you to repeat the image to as large a size as you need - without loss of quality for printing.