Hi again @Joe_Nguyen 
Here is how you can do this using a the below-site-header plugin outlet.
Step 1: In common-head of a theme or theme component put this:
<script type="text/x-handlebars" data-template-name="connectors/below-site-header/header-color-bar">
<div id="color-bar">
</div>
</script>
Step 2: In common-css of the same theme or theme component, put this:
#color-bar {
background-color: #13d83d;
height: 30px;
}
note: you can adjust the height and change color property to whatever you want.
That should do it: 
