At the moment, if you try to customize the CSS for a, a:hover, a:active and a:visited in our custom css file it does not overwrite the default CSS. If we add "!important" to the CSS styles then it overwrites the text color for button styles. There are times when the primary color does not work well as a link color or is not ADA compliant.
I would like to suggest in a future version of Porto that the main link color be customizable. Either through the style switcher or another method (custom CSS file).
Porto 5 will have this feature.