Denim, it's an absolute staple, and these days you can wear jeans anywhere. But, having the correct colors for the work is essential. I don't advise all denim colors for every occasion, so you should understand not only what 4 colors you need to wear, but also the correct and incorrect moments. I suggest owning the four denim colors are dark indigo, a brighter blue, gray and black wash.
I enjoy a nice black jeans couple and it's almost as essential to your wardrobe as dark indigo jeans. They have a lot of a rocker atmosphere and look good for occasions during the night. With a couple of black jeans, a white or gray shirt, and a couple of sneakers or shoes, you can never go wrong.
While not as important as dark wash jeans, it may be quite flexible to use gray jeans. Stick with a grey wash medium to darker and don't worry about dressing them up. Think of them in terms of how and where you'd wear them like a couple of gray chinos.
Light Wash Jeans
Not as versatile as a darker wash, for more casual circumstances I suggest a lighter blue. Be cautious not to go too fast on the wash as the colors of very light tend to be a little too trendy and maybe a little too young.
If you have only one pair, you have a dark indigo wash, so buy these first! It is the most versatile and dressed in something like a blazer and loafers or with everything casual like sneakers and a t-shirt. If you're working in a casual company office, dark indigo jeans are an excellent option for casual days for chinos.