I’ve never thought of this, but Darcy Clarke proved you can customize the WebKit Inspector (and Chrome dev tools) simply by editing your user stylesheet. Check the post and comments for some examples of syntax highlighting themes. Neat!
Considering my WebKit Inspector wish list, I added some styles to clean up and improve the styles panel – including moving the enable/disable checkboxes to the left (this is actually being implemented as well). Now that user agent styles can be hidden and Alexander Pavlov is implementing different highlight colors for paddings and margins, the wish list is getting a lot shorter!