here’s the code:

::selection {
        background: #ffb7b7; /* Safari */
        }
::-moz-selection {
        background: #ffb7b7; /* Firefox */
}

just change the numbers using the color palette

paste it right before the </style> tag in your theme

to look for the tag just press Ctrl and F together and type </style>

and paste the codes right after that highlighted part! :D

(Source: ricapturethemoments)