I was able to change the lightbox colors and text by adding code to the head code section like so:
<style>
/* turning the lightbox background to white */
.w-lightbox-backdrop {background: rgba(256,256,256,.9);}
/* turning the slide buttons orange */
.w-slider-dot {
background: rgba(219,97,11,0.5); font-size: 16px;}
.w-slider-dot.w-active {
background: rgba(249, 209, 80,0.5);
font-size: 16px;}
/* turning the lightbox text colors */
.w-lightbox-backdrop {
position: fixed;
top: 0;
right: 0;
bottom: 0;
left: 0;
color: #fff;
font-family: "pragmatica-web", Helvetica, Ubuntu, "Segoe UI", Verdana, sans-serif;
font-size: 18px;
font-weight: 400;
</style>`