It's not as though she turned up in bridal white complete with freesias and train. How was Sarah Baillie supposed to know what Kate would be wearing? Had the Duchess posted a status update on her Facebook page "Digging out the old blue tweed for Lucy's bash"?
At least the Mirror came up with an amusing headline.
Just in case you commit the unforgiveable social error of appearing at morning conference in the same pink Ben Sherman shirt as the editor, here is the SubScribe etiquette to cover the faux pas. When you see he's spotted the clash, feign surprise and look down at yourself and up at him with a sheepish or conspiratorial smile (depending on the boss).