Convert Color Hex Values To RGB Using Php

I'm looking for a script that will search through style sheets and replace colors defined with hex values (ex: color:#FFFFFF) with its rgb value (ex: color:rgb(255,255,255)). There will also be a mixture of named colors (ex: color:white) and rgb values already in the style sheets so it will need to skip over those. I need this done ASAP. Please let me know if you have any questions.