2 types of grey shirt:

1.  The Cromptoneque iGent grey shirt, usually worn with a double breasted Neapolitan jacket with patch pockets, a grenadine tie, trousers with excessively large turnups, and no socks.  In short, the calling card of a knob-head.

2.  The grey shirt from man-made fibres, worn with M&S grey suit purchased in 1997 and matched with grey polyester tie, worn by a 50 year old mid-ranking member of the account department called Phil.

If we're talking very light gray, lighter than pale blue shirts, it can work for Asian complexions, and austere minimalist types, preferably with gray hair.  There is still the risk of looking too Regis Philbin monochrome, but it can be pulled off by some.  If we're talking dark gray stuff, that will always make one look like a coal miner.

Grey shirts? Bad idea. Better stock up on good deodorant because nothing will show sweat like a grey shirt.

Grey is a beautiful colour for a suit though.

Horrible for shoes.

My own preference is for mid to dark grey, not charcoal. Light greys can look a little washed out to my eye.

Saying that though, light grey flannel trousers are useful because they allow you to use lighter coloured jackets whilst maintaining contrast.