personally, i have never been a huge fan of the critique, "this is nice, BUT, would look better with different color PS/pants/socks/underwear......"
imo, many times, if it looks good, it looks good. maybe the person has a certain item, and they want to wear it. or they got sick of gray/brown pants and wanted a new color. its like saying, you look good, but it would be even better if you were wearing a totally different outfit that also looks good, but might be better (well that is an exaggeration).
There's absolutely nothing wrong with saying to someone that one element of their otherwise perfectly formed outfit is off - indeed that is often the most helpful thing to me - sometimes I really didn't realise that the trousers I had chosen looked even worse than I had throught. Okay, so the fact that sometimes we already know that this is a problem might make it annoying to have it pointed out, but if we don't want anyone to say anything, why post in this thread at all? And even if you or I don't think we need to be told - and personally, I'm not sure I can claim that - it certainly helps other people to understand what works and what doesn't.