How to change preloader background?

This feature is not available in theme at present moment, but you can change in by means of css code.

Paste this code at the bottom in style.css file (navigate through Appearance=>Editor).

.body-preloader { background: your_color !important; }
.inner-preloader { background: your_color !important; }

If you want to add background image for preloader, add this code in style.css

.body-preloader { background-image: url('link to image') !important; }
.inner-preloader { background-image: url('link to image') !important; }