To change the color of the top and bottom bars, go to
Graphene Options >> Colors >> Slider
To change the color of the background of the post title and description:
.slider-entry-wrap {background: #000;}
To change the color of the post title in the slider:
.slider_post h2 { background: #000;}
To change the color of the post description in the slider:
slider_post_entry {background: #000;}
Add all CSS changes to Custom CSS feature in Graphene or child theme stylesheet.