Hexadecimal is the main way to make colours in a lot of programming languages and is not so much a different colour as it is a more precise and accurate way to make a colour.
Felix Well in html, CSS, it's best to use hex colours because it's more precise for the browsers need. If you just type 'colour:blue' it won't be the same in every browser. But if you type it in hex. Then you've got a precise colour for all browsers