I-N in and O-U-T out!!!
First of all, leggings are in the stage where thay are not exactly O-U-T out but aren't exactly I-N in either. At this point, this is regarding any clothing, accessorie, fashion item, etc., you should just not wear it anymore. So don't. Anyway, you can wear gray(grey)(whatev) denim jeans anywhere so they double as a casual pant or a jean (dressy or casual).
REMEMBER: These type of bottoms are not IN if they aren't rocker-esque. So They have to be completely cigarette type and hug your every curve by being stretch and tight (thank god for 2% spandex).
I went through a couple of websites and found the best grey denim jeans ever... They can be found at www.shopbop.com:
These jeans are Sass and Bide one of the most sought after brands for jeans by the elite such as Kate Moss and Hilary Duff. They are the Frayed Misfits Stove Pipe Jean Stretch for $231. The left is in faded black while the right is in gunmetal.