How did you make that cool trick with the PowerMag logo changing color?

Well that’s kind of a trick for demo purposes, good news is that your theme is already set up to do the same if you want to! 
The PowerMag logo is basically a transparent png file where the word “Mag” is a ‘hole’ and the div background color changes according to the category color. To replicate it without editing theme files you should add the following in the Advanced tab and enter:

Custom JS

(adds .demologo class to the logo image, do not change the class name):

jQuery(document).ready(function($) {
  $('#logo a').addClass('demologo');
});

Custom CSS:

.demologo {
display: block;
width: 202px;
height: 67px;
margin: 0 auto;
}

Finally edit the width and height of .demologo with your logo size.