isDark

/*
 * Find if a background is dark or light and define text color.
 * Created by Adriano Caheté <https://github.com/AdrianoCahete>
 */
$(document).ready(function () {
	function isDark(color) {
		var match = /rgb\((\d+).*?(\d+).*?(\d+)\)/.exec(color);
		var r = parseInt(match[1]);
		var g = parseInt(match[2]);
		var b = parseInt(match[3]);
		var yiq = (r * 299 + g * 587 + b * 114) / 1000;
		return (yiq <= 128);
	}

	var divs = $(".color-item");
	$(divs).each(function () {
		$(this).css("color", isDark($(this).css("background-color")) ? 'white' : 'black');
	});
});

In HTML:
<div class="color-item" style="background-color:#3C3C3C;">#3C3C3C</div>
<div class="color-item" style="background-color:#FFFFFF;">#FFFFFF</div>