You don't need to edit the script. Put this stylesheet in the head of the page:
or put its rules in an existing stylesheet for the page.
Be sure to use the !important keyword as shown. That overrides the script's default styles for those elements.
A note about the background color though, because it is transparent, it's a bit lighter than a solid version of the color would be. So - say for pink, you might want to use red. Also, if you want to have different colors for different slideshows on the same page, you can prefix the class names above with the wrapper id of each show, ex: