It's simple.
Connect this plugin to your page:
<script src="/path/to/invertImgText.js"></script>
<!-- HTML -->
<div class="patt" id="patt1">
Lorem ipsum dolor sit amet.
</div>
...
/* CSS */
#patt1{
background: url('img/congruent_outline.png') 0 0 repeat;
}
...
AND
JavaScript:
// get background image on this block
$('.patt').invertImgText();
or
$('.patt').invertImgText('/path/to/img.jpg');
Text color in .patt block will be changed