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hex color values like #fff or #ffffff are not recognized by the current CVS version of the CSS Validator, org.w3c.css.properties.CssColorCSS1 and org.w3c.css.properties.CssColorCSS2 test for val instanceof org.w3c.css.values.CssColorCSS1 /* or the respective */ val instanceof org.w3c.css.values.CssColorCSS2 while 'val' is only an instanceof org.w3c.css.values.CssColor. See http://www.w3.org/mid/3f1672c2.211378896@smtp.bjoern.hoehrmann.de
Looks like the problem has been fixed for color, but not background or border.