Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="box grayscale" data-label="Gray"></div>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script>
<script src="http://kununu.github.io/gray/js/jquery.gray.js"></script>

SassMeister-input.sass

// ----
// Sass (v3.3.6)
// Compass (v1.0.0.alpha.18)
// ----

@import "http://kununu.github.io/gray/css/gray.css"

.box
  background-image: url(http://stanford-guitars.com/wp-content/themes/elbworx-starter/assets/img/frontpage/durango-series-bg-image-hover.jpg?1398150271)
  background-size: cover
  background-position: center
  display: inline-block
  width: 400px
  height: 400px

.grayscale:hover
  -webkit-filter: grayscale(0%)
  filter: none

SassMeister-output.css

@import url(http://kununu.github.io/gray/css/gray.css);
.box {
  background-image: url(http://stanford-guitars.com/wp-content/themes/elbworx-starter/assets/img/frontpage/durango-series-bg-image-hover.jpg?1398150271);
  background-size: cover;
  background-position: center;
  display: inline-block;
  width: 400px;
  height: 400px;
}

.grayscale:hover {
  -webkit-filter: grayscale(0%);
  filter: none;
}

SassMeister-rendered.html

<div class="box grayscale" data-label="Gray"></div>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script>
<script src="http://kununu.github.io/gray/js/jquery.gray.js"></script>