find hex color
HTML
<b id="output"></b>
JavaScript
var re = /#([a-f0-9]{3}){1,2}\b/gi;
var str = "color: #3f3; background-color: #AA00ef; back: #abcd";
document.getElementById('output').innerHTML = str.match(re);
<b id="output"></b>
var re = /#([a-f0-9]{3}){1,2}\b/gi;
var str = "color: #3f3; background-color: #AA00ef; back: #abcd";
document.getElementById('output').innerHTML = str.match(re);