> **This is your solution**
<!-- begin snippet: js hide: false console: true babel: false -->
<!-- language: lang-css -->
.navbar-nav .services-link:hover{
color: #7FFF00 !important; /* your color */
}
<!-- language: lang-html -->
<html>
<head>
<title>Contact Us</title>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
<link href="contact.css" type="text/css">
</head>
<body>
<div class="container-fullwidth">
<nav class="navbar navbar-expand-lg navbar-dark bg-success fixed-top">
<h1 class="navbar-brand"><strong>Digitian Hub</strong></h1>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#NewMenu" aria-expanded="false" aria-controls="NewMenu" aria-label="toggleNavigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="NewMenu">
<div class="navbar-nav">
<a class="nav-item nav-link" href="Rishabh.html"><strong>Home</strong></a>
<a class="nav-item nav-link services-link" href="#"><strong>Services</strong></a>
<a class="nav-item active nav-link contact-link" href="Contact Us.html"><strong>Contact Us</strong></a>
</div>
</div>
</nav>
</div>
</body>
</html>
<!-- end snippet -->
Add below **CSS** for adding hover to navigation and add after **bootstrap CSS** in header
.navbar-dark .navbar-nav .nav-link.services-link:hover {
color: rgba(0,255,0,1);
}
<!-- begin snippet: js hide: false console: true babel: false -->
<!-- language: lang-html -->
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
<link href="contact.css" type="text/css">
<style type="text/css">
.navbar-dark .navbar-nav .nav-link.services-link:hover {
color: rgba(0,255,0,1);
}
</style>
<div class="container-fullwidth">
<nav class="navbar navbar-expand-lg navbar-dark bg-success fixed-top">
<h1 class="navbar-brand"><strong>Digitian Hub</strong></h1>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#NewMenu" aria-expanded="false" aria-controls="NewMenu" aria-label="toggleNavigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="NewMenu">
<div class="navbar-nav">
<a class="nav-item nav-link" href="Rishabh.html"><strong>Home</strong></a>
<a class="nav-item nav-link services-link" href="#"><strong>Services</strong></a>
<a class="nav-item active nav-link contact-link" href="Contact Us.html"><strong>Contact Us</strong></a>
</div>
</div>
</nav>
</div>
<!-- end snippet -->