Hello Ciaran,
I tried to change the color of the social media icons on J4 Nina.
Changing the hex value in the option in the template does not make any difference. It stays #fff
That's because the nexus.min.css changes the color to white:

.socialmedia ul li a [class^="fa-"]::before, .socialmedia ul li a [class*=" fa-"]::before {

  position: relative;

  padding-right: 0;

  color: #fff;

}

For me changing the color value to "inherit" in the custom.css does work.

.socialmedia ul li a [class^="fa-"]::before, .socialmedia ul li a [class*=" fa-"]::before {color: inherit;}

Maybe deleting the color property in the nexus.min.css would be a solution?
I only want to bring this to your attention.

Regards
Oliver