Both involving watercolour washes, which will you try? Why not both?
Details on the following links:
http://trishbee.wordpress.com/2009/05/02/bright-watercolour-wash-crayon-backgrounds/
http://trishbee.wordpress.com/2009/05/04/watercolour-wash-backgrounds-part-2/
Might be adding another one yet so watch this space!
