Change Bootstrap tooltip color

You can use this way:

<a href="#" data-toggle="tooltip" data-placement="bottom"
   title="" data-original-title="Tooltip on bottom"
   class="red-tooltip">Tooltip on bottom</a>

And in the CSS:

.tooltip-arrow,
.red-tooltip + .tooltip > .tooltip-inner {background-color: #f00;}

jsFiddle


Moeen MH: With the most recent version of bootstrap, you may need to do this in order to get rid of black arrow:

.red-tooltip + .tooltip.top > .tooltip-arrow {background-color: #f00;}

Use this for Bootstrap 4:

.bs-tooltip-auto[x-placement^=bottom] .arrow::before,
.bs-tooltip-bottom .arrow::before {
  border-bottom-color: #f00; /* Red */
}

Full Snippet:

$(function() {
  $('[data-toggle="tooltip"]').tooltip()
})
.tooltip-main {
  width: 15px;
  height: 15px;
  border-radius: 50%;
  font-weight: 700;
  background: #f3f3f3;
  border: 1px solid #737373;
  color: #737373;
  margin: 4px 121px 0 5px;
  float: right;
  text-align: left !important;
}

.tooltip-qm {
  float: left;
  margin: -2px 0px 3px 4px;
  font-size: 12px;
}

.tooltip-inner {
  max-width: 236px !important;
  height: 76px;
  font-size: 12px;
  padding: 10px 15px 10px 20px;
  background: #FFFFFF;
  color: rgba(0, 0, 0, .7);
  border: 1px solid #737373;
  text-align: left;
}

.tooltip.show {
  opacity: 1;
}

.bs-tooltip-auto[x-placement^=bottom] .arrow::before,
.bs-tooltip-bottom .arrow::before {
  border-bottom-color: #f00;
  /* Red */
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.bundle.min.js"></script>
<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" rel="stylesheet" />
<div class="tooltip-main" data-toggle="tooltip" data-placement="top" data-original-title="Hello world"><span class="tooltip-qm">?</span></div>
<style>
  .bs-tooltip-auto[x-placement^=bottom] .arrow::before,
  .bs-tooltip-bottom .arrow::before {
    border-bottom-color: #f00;
    /* Red */
  }
</style>

Bootstrap 2

If you want to change the caret/arrow as well, do the following:

.red-tooltip + .tooltip > .tooltip-inner {background-color: #f00;}
.red-tooltip + .tooltip > .tooltip-arrow {border-bottom-color: #f00;}

or

.red-tooltip + .tooltip > .tooltip-inner, .red-tooltip + .tooltip > .tooltip-arrow {background-color: #f00;}

jsFiddle: http://jsfiddle.net/technotarek/2htZe/

UPDATE: Bootstrap 3

You have to be specific for the direction of the tooltip in Bootstrap 3. For example:

.tooltip.top .tooltip-inner {
    background-color:red;
}
.tooltip.top .tooltip-arrow {
      border-top-color: red;
}

jsFiddle for all tooltip directions using Bootstrap 3: http://jsfiddle.net/technotarek/L2rLE/