Artwork is a matter of taste, style and consistency. Design by committee does not work.
If we really want to get a consistent, stylish and professional Debian style trough the whole Debian (and I think we should), we need to have an appointed Debian artwork czar - a professional designer or graphic artist, who would agree to dedicate some of his time on continuous basis to creation and improvement of Debian artwork and refinement of the old artwork from release to release. In exchange he would get to show of his elite design skillz via Debian to a lot of users across the world.
Formally he would have to be a DPL deputy and have the ultimate say about all artwork and colour related matters. I think the DPL should organise this.