Hi there!
Thanks for contacting us.
If you are talking about the active menu item color then you will find the custom style option within the Preset tab of your template options.
If you are talking about the background color of it then it is designed to make it different in some of our templates, so we have taken the opportunity, and hence custom CSS is always an option for you. Here is a sample code for you:
.sp-megamenu-parent >li.active>a, .sp-megamenu-parent >li:hover>a {
background: green !important;
}
You can put any color within the above code as per your need.
Note: Path towards custom CSS: Extensions>Templates>Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.
Best Regards