yep you’ve got the right idea!
something like this,
also changes the underline on hover color,
chuck it in your child theme’s style.css ??
a,
.entry-content a {
color:purple;
}
.entry-content a:hover{
color:pink;
border-bottom-color: pink;
}
.header-menu .current-menu-item > a {
border-bottom-color: purple;
color: purple;
}
.header-menu .current-menu-item > a:hover {
border-bottom-color: pink;
color: pink;
}