Available text color classes in Bootstrap

The bootstrap 3 documentation lists this under helper classes: Muted, Primary, Success, Info, Warning, Danger.

The bootstrap 4 documentation lists this under utilities -> color, and has more options: primary, secondary, success, danger, warning, info, light, dark, muted, white.

To access them one uses the class text-[class-name]

So, if I want the primary text color for example I would do something like this:

<p class="text-primary">This text is the primary color.</p>

This is not a huge number of choices, but it's some.

The text at the navigation bar is normally colored by using one of the two following css classes in the bootstrap.css file.

Firstly, in case of using a default navigation bar (the gray one), the .navbar-default class will be used and the text is colored as dark gray.

.navbar-default .navbar-text {
  color: #777;
}

The other is in case of using an inverse navigation bar (the black one), the text is colored as gray60.

.navbar-inverse .navbar-text {
  color: #999;
}

So, you can change its color as you wish. However, I would recommend you to use a separate css file to change it.

NOTE: you could also use the customizer provided by Twitter Bootstrap, in the Navbar section.