Hello @kuyman ,
Yes, you can use a single slide as a banner. To get the parallax effect as an inner banner to home slide, please add Additional CSS. For that, go to Dashboard > Appearance > Customize > Additional CSS and paste below code:
.block-slider .slide-item {
-webkit-background-attachment: fixed;
-moz-background-attachment: fixed;
-ms-background-attachment: fixed;
-o-background-attachment: fixed;
}
And regarding the banner overlay color change, you did on the right way. Thanks.
Best Regards.