Back in my Kindergarten times we used a special technique to "paint" pictures. First we would take a blank piece of paper and fill it with random bright colours (coloured pencils) then we would take a black wax crayon and cover the whole page so nothing could be seen any more. After that we would take a tooth-pick and scratch away lines through the wax and the bright colours would shine through.
Eventually this would lead to a mostly black picture consisting of colourful lines.
Does anybody know what I am babbling about? Is there a name for this?
FWIW: It is easily possible to recreate that effect in AR 2.5 by simply adding a layer (filled with black wax) and using the eraser tool.