en.javascript.info/9-regular-expressions/09-regexp-quantifiers/2-find-html-colors-6hex/solution.md

We need to look for # followed by 6 hexadecimal characters.

A hexadecimal character can be described as pattern:[0-9a-fA-F]. Or if we use the pattern:i flag, then just pattern:[0-9a-f].

Then we can look for 6 of them using the quantifier pattern:{6}.

As a result, we have the regexp: pattern:/#[a-f0-9]{6}/gi.

let regexp = /#[a-f0-9]{6}/gi;

let str = "color:#121212; background-color:#AA00ef bad-colors:f#fddee #fd2"

alert( str.match(regexp) );  // #121212,#AA00ef

The problem is that it finds the color in longer sequences:

alert( "#12345678".match( /#[a-f0-9]{6}/gi ) ) // #12345678

To fix that, we can add pattern:\b to the end:

// color
alert( "#123456".match( /#[a-f0-9]{6}\b/gi ) ); // #123456

// not a color
alert( "#12345678".match( /#[a-f0-9]{6}\b/gi ) ); // null