painting a bump map in texture pain mode does not work.

When I try painting a bump map in 3D view I only get the color of the brush is set at without any bump of any kind. However, if I try painting, without changing any settings, in the image viewer it works as normal. I would do that but it is hard painting on a solid black picture :confused:
Any clues as to what could be going on?

See this tutorial for help