Thumb gallery it's a new addon inside SP Page Builder collection. The gallery have a view it with the thumbnail carousel. It shows big image and collection of small one (thumbs) under, they are presented one by one.

If you want to remove dark layer from all thumbs please use following CSS code inside custom.css file:

.sppb-addon-thumb-gallery #carousel ul li { opacity: 1; }
.sppb-addon-thumb-gallery #carousel ul li::after { background-color: transparent;}