letter color in bootstrap code example

Example 1: bootstrap 4 text color

<p class="text-primary">Text with primary color</p>
<p class="text-secondary">Text with secondary color</p>
<p class="text-success">Text with success color</p>
<p class="text-danger">Text with danger color</p>
<p class="text-warning">Text with warning color</p>
<p class="text-info">Text with info color</p>
<p class="text-light bg-dark">Text with light color</p>
<p class="text-dark">Text with dark color</p>
<p class="text-muted">Text with muted color</p>
<p class="text-white bg-dark">Text with white color</p>

Example 2: bootstrap color a div

use something like :
<div class="container alert alert-success">
   <div class="row">
      <div class="col">I'm your content inside the grid!</div>
   </div>
</div>