Answer to Avada Forum Post https://theme-fusion.com/forums/topic/fusion-slider-darken-an-image/
Just in case you don't find a Fusion Builder setting (doubt there is one). And, without seeing your page, here's an example that will work for the hero image on this page.
https://marklchaves.com/responsive-banner-hero-image-demo/
.hero {
background-image: linear-gradient(
rgba(0, 0, 0, 0.3),