After fiddling around with the CSS, I was able to remove the texture and darkening of the image with these two changes.
First, find this in your CSS:
.flickity-viewport:after {
background-color: rgba(0, 0, 0, 0.3);
background-image: url("{{ 'overlay_pattern.png' | theme_image_url }}");
background-repeat: repeat;
background-size: 4px;
content: "";
height: 100%;
position: absolute;
top: 0;
width: 100%;
z-index: 1;
}
Now, you're going to want to remove this line entirely to remove the textured overlay:
background-image: url("{{ 'overlay_pattern.png' | theme_image_url }}");
To remove the image darkening, simply change this:
background-color: rgba(0, 0, 0, 0.3);
To this:
background-color: rgba(0, 0, 0, 0);
Your slideshow images should appear normal with those two changes.