Okay, so here is the interim solution: keep in mind this is not upgrade proof and you will loose this change if you update the template.
Instructions are straight forward:
1. Go to templates/gk_quark/layouts
2. Open 'default.php'
3. Go To Line 155, it will look like: #gk-page-preloader { background: #1f4196 url('<?php...
4. Change the background colour to whatever you want (the 6 character code after the # sign)
5. Save
6. Refresh your home page and enjoy the colour.
I tried this in the overides (new and old css) to no avail, so if there is a more permanent way I am all eyes looking for it.
J.