In order to change the color of a highlight bar, you need to go into the app factory and add a highlight block.   Once you have the highlight block, click on the gear to open up editing options. 

In your editing options, choose the <> option to edit your html.

You will need to add in the following html.  The XXX's are where you should place your text. You will need to change your background color and font color with hex colors.  

<div style="text-align: center; background-color: #95d600; color: #ffffff;"><span style="font-size: 2em;">XXX</span><br /><span style="font-size: 1.5em;"></span></div>