I've finished a new stylesheet for the site - it's green and goes by the name Pelouse.
I've also begun cleaning up the sheets so that colours only get declared in <colourname>.css files. All other sheets only deal with layout, typography etc. This keeps the site looking the same in terms of layout no matter the colour scheme.
I'll finish the de-crufting of layout sheets next and begin working on a brown sheet (Bois?) after that. The last step will be tidying up the original and versailles sheets.