Use Vibrant.js to extract foreground and background colours from images (uses http://jariz.github.io/vibrant.js/)

extract-image-colours.js

(function ($) {
	$(document).ready(function () {
		$('.image-to-colour').each(function (index, element) {
			var images = $(this).find('img');
			if (images.length == 1) {
				var imageColours = getImageColours(images[0]);
				element.style.color = imageColours.textColour;
				element.style.backgroundColor = imageColours.backgroundColour;
			}
		});
	});

	// Get suitable background and foreground colours from image
	function getImageColours(image) {
		var vibrant = new Vibrant(image);
		var swatches = vibrant.swatches();
		return {
			backgroundColour: (swatches.LightMuted) ? swatches.LightMuted.getHex() : ((swatches.LightVibrant) ? swatches.LightVibrant.getHex() : '#fff'),
			textColour: (swatches.LightMuted) ? swatches.LightMuted.getTitleTextColor() : ((swatches.LightVibrant) ? swatches.LightVibrant.getTitleTextColor() : '#000')
		}
	}
})(jQuery);