Since you’re using the dark blue theme, you can find the color on line 2975 in your css –
.epik-darkblue .genesis-nav-menu a {
color: #fff;
}
If you change that it will affect all of your menu links, including your main menu. So I would add this to your css instead –
.epik-darkblue .nav-secondary .genesis-nav-menu a {
color: #293f5e;
}
and that will change just the Secondary Nav by itself.