It looks like you don’t just have a single stylesheet, there is some CSS hardcoded into your theme files too?
Is there something that looks like this in your header.php
file?
<style type="text/css" media="all">
body { background:#636566 url("https://www.myanimeisland.com/wp-content/themes/eximiusBlack/images/background.gif") repeat-x; }
#header { background: url("https://www.myanimeisland.com/wp-content/themes/eximiusBlack/images/newmai.jpg") no-repeat ; }
#header { height: 250px; }
</style>
Any CSS in your template files would override the CSS in your stylesheet, so I think that is the problem.
If you can find that code above in your header file, you could edit it there to make the change actually show up. However, there is a background image and color, so the image will cover up the color. You either need to change both or remove the image and just set a color for the background.