This is what I've just figured out, but you have to put it into the code injection footer section, between style tags, for it to last more than 1 second.
.social-icons-style-knockout.social-icons-color-black .sqs-use--mask {fill: #42afc2;}.social-icons-style-knockout.social-icons-color-black:hover .sqs-svg-icon--wrapper:hover .sqs-use--mask {fill:#42afc2}
This changes the hover color as well, though I haven't been able to figure out the gray hover color in between.
my site: https://helen-skiba.squarespace.com/