p.s. I forgot to mention: I'm not sure if it's possible for the colors in G2G to be modified. It's actually a separate site than WikiTree, and it's not as easily modified. We'll still make a note of your feedback, though, just in case! :-)
p.p.s. I realize you are using Safari ... looking for a way to adjust the color of visited links. I have a MacBook, too, but I don't see anything in preferences for Safari that allows you to do that.