WPrefs: grouped items related to the color selection in a single place
Having all these information spread in different places makes it error
prone when wanting to add/remove/change something in the list are there are
many unrelated places to keep in sync.
By merging everything in a single struct array it is a lot easier to
maintain this list.
Took the opportunity to properly document a little hack which is used to
avoid complex handling for a special case.
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>