Are you able to edit your theme stylesheet? It should be something like style.css in the main directory of your theme folder. If so, you need to edit, or add, the CSS pseudo-class a:hover and define a color.
Here is an explanation from W3Schools, where you can even try it yourself from their site:
https://w3schools.com/css/css_pseudo_classes.asp
That site is a great start if you are looking for an introduction to CSS. Hope that helps!