Since you’re using an older version of the theme, you’d need to use child theme to safely modify the colour without losing the modification the next time you update.
Insert this code into your child theme’s style.css file:
#previous, #previous a, #previous a:visited, #next-post, #next-post a, #next-post a:visited {
color: #929292;
}
Change the colour value to whatever colour you want.