I was flustered by this image overlay issue, too. My "card" images were greyed-out, looked terrible. After checking out the CSS, I found a solution and added this snippet to Design > Custom CSS:
.sqs-block-image .image-overlay, .sqs-block-image .sqs-image-content::after, .sqs-block-image .image-block-wrapper::after {
opacity: 0;
}
Originally, the default opacity was set to 0.1, which was causing the "grey-out" problem. As soon as I pasted in this CSS, all of the grey image overlays in my cards disappeared.
If anybody else is able to clear up their image display issues with this CSS, please let me know. I've written to support, too, so hopefully they'll look into it.