Monochrome safe. The many shades of grey is a plus. Similar to the flexibility of wearing black and white, it brings a whole different element to your look. Doesn't matter what your skin tone is grey is going to look good on you. Although, it's not that simple; it also depends on which complimenting colors and different cuts you choose to wear. It is appropriate to wear in pretty much any occasion, unless it's a black-tie event or any other specific dress code event.
Things to keep in mind if you do decide to sport some grey, after you make sure your clothes fit you properly (fit should always be your first priority). Remember, the shades come in dark and light, this means your other items cannot fall into the same shade. Unless you are putting on a complete grey suit, the other items in your look should have the opposite shade. In other words, if it's something dark, you pair it with something lighter and vice versa. These should come off as common sense to most and are very basic, but many of us tend to forget the basics and completely disregard the first things we learn.
You could go all out grey in different shades but what really catches the eye is putting it together with an unexpected color. Think purple or a darker shade of green. You can also go with patterns but that can be very tricky. You'll have to really know your stuff or I'll have to post something on that topic in the future. Now, when I think grey, for some odd reason, I think cardigan. I've posted a bunch of 'grey' items that you can work an entire outfit around...starting with cardigans.
Click image captions for more info.

Topman mid grey slim placket cardigan

BLK DNM cashmere cardigan

PS by Paul Smith double-breasted wool cardigan

Gant Rugger unstructured cotton-piqué blazer

Topman grey Hugo skinny blazer

H&M wool jacket

Burberry London slim-fit cotton shirt

H&M marled flannel shirt

Zara stretch shirt

Dolce & Gabbana long-sleeve henley

H&M henley shirt

Zara piqué polo w/ peter pan collar

Acne - Roc Marden slim-fit jeans

H&M slim low jeans

Topman grey wash vintage slim jeans

Burberry London slim-fit wool trousers

Zara checked trousers

Topman grey Vento tweed skinny trousers

Common Projects - Chukka suede boots

Zara - Street Oxford shoe

Quoddy suede boat shoes