[css-colors] references an inexistant property

There’s a problem in the current [css-colors] draft because it deprecated System Colors and ask to use the ‘appearance’ property instead (which I used to love but which has been removed from the latest [css-ui] drafts).



We should therefore remove the following remark from the [css-colors] spec :

| Note. The CSS2 System Color values have been deprecated in 
| favor of the CSS3 UI ‘appearance’ property. If you want to emulate
| the look of a user interface related element or control, please use
| the ‘appearance’ property instead of attempting to mimic a user
| interface element through a combination of system colors.

Regards,
François