Hello Ferlin,
Yes, you can add a background color to the rating but it is not advisable since it will looks weird. However, you want to try, you can add this css code to your template css file:
#eblog-wrapper .blog-rating form > div
{
background-color: #000000 !important;
}
Other way, you can edit the rating file itself:
../components/com_easyblog/themes/default/blog.rating.php Or you can edit the image here:
/components/com_easyblog/assets/vendors/ratings/stars.png. Hope this helps.