To change these colors, or any other color or styling on your website, first right-click on the element, and choose "Inspect" menu from your browser.
That will display you the CSS properties that influence the display of that element.
Then add those CSS lines either in your Joomla template, or in CB plugin "Default" template, "overrides" tab.
In this later case, current 2 CSS rules will override the default colors with red (#F00) and green for highlighted ones (#0F0):
Code:
.cb_template .navbar-light .navbar-nav .nav-link {
color: #F00;
}
.cb_template .navbar-light .navbar-nav .show > .nav-link, .cb_template .navbar-light .navbar-nav .active > .nav-link, .cb_template .navbar-light .navbar-nav .nav-link.show, .cb_template .navbar-light .navbar-nav .nav-link.active {
color: #0F0;
}