HTML

bootstarp btn colors

<button type="button" class="btn btn-primary">Blue</button>
<button type="button" class="btn btn-secondary">Grey</button>
<button type="button" class="btn btn-success">Green</button>
<button type="button" class="btn btn-danger">Red</button>
<button type="button" class="btn btn-warning">Yellow</button>
<button type="button" class="btn btn-info">Ligth blue</button>
<button type="button" class="btn btn-light">White</button>
<button type="button" class="btn btn-dark">Black</button>

<button type="button" class="btn btn-link">White with blue text</button>

custom color bootstrap buttonm

.btn-primary, .btn-primary:hover, .btn-primary:active, .btn-primary:visited {
    background-color: #8064A2 !important;
}

bootstrap btn colors

<!-- Bootstrap v5.0 -->

<button type="button" class="btn btn-primary">Primary</button>
<button type="button" class="btn btn-secondary">Secondary</button>
<button type="button" class="btn btn-success">Success</button>
<button type="button" class="btn btn-danger">Danger</button>
<button type="button" class="btn btn-warning">Warning</button>
<button type="button" class="btn btn-info">Info</button>
<button type="button" class="btn btn-light">Light</button>
<button type="button" class="btn btn-dark">Dark</button>

<button type="button" class="btn btn-link">Link</button>

btn-default class in bootstrap 4

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">

<div class="container m-3">
    <a class="btn btn-outline-secondary">outline-secondary link</a>
    <button type="button" class="btn btn-outline-secondary">outline-secondary 'button'</button>
    <br><br>
    <a class="btn btn-outline-light">outline-light link</a>
    <button type="button" class="btn btn-outline-light">outline-light 'button'</button>
</div>

Group Buttons in Bootstrap Red Yellow Green

<div class="btn-group" role="group" aria-label="Basic outlined example">
  <button type="button" class="btn btn-outline-primary">Left</button> 
  <button type="button" class="btn btn-outline-primary">Middle</button>
  <button type="button" class="btn btn-outline-primary">Right</button>
</div>

Bootstrap custom button color

.btn-primary, .btn-primary:hover, .btn-primary:active, .btn-primary:visited {
    background-color: #8064A2;
}