Setting Font Color Based on Background Color

This isn't anything pressing, just a shot at an enhancement that would be pretty darn cool if I could get it to work right.  We have an application that allows its users to set the background color of a content area.  The text is black, so if you select a dark color, there are major contrast issues.  Up until now, we've asked the users to manually set the font color via the inline editor to correct the contrast issue.  On a whim, I threw something together that I thought would rightly handle the contrast issue on the fly.  For the most part, it works, but there are exceptions.  Basically, what I am doing is checking the NaN of the first character of the hex value that the user chooses for the background.  If it's a number, of if it is 'f', I set the font color to black.  Otherwise, I set the font color to white.  Has anyone done something like this and worked out all of the 'exceptions'?  The boss doesn't feel like we should spend any more time on it, since we have other more pressing issues, but I'd sure like to see it work.  :)

Here's my code:
$('#contentCallBack').jPicker(
	{},
	function(color, context){
		var all = color.val('all');
		$('#layoutBG').attr('bgcolor',(all && '#' + all.hex));
		$('#sideBarGBG').attr('bgcolor',(all && '#' + all.hex));
		var positionOne = all.hex.substring(0,1);
		if(isNaN(positionOne) == false || positionOne == 'f'){
			$('#layoutBG').css({
				color: '#ffffff'
			});
		} else {
			$('#layoutBG').css({
				color: '#000000'
			});
		}
	},
	function(color, context){
		if (context == layoutBGCallbackButton.get(0)) alert('Color set from button');
		var hex = color.val('hex');
		layoutBGCallbackElement.css({
			backgroundColor: hex && '#' + hex || 'transparent'
		});
	},
	function(color, context){
		//alert('"Cancel" Button Clicked');
	}
);

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brianmfallsAsked:
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Lee SavidgeCommented:
If you have a function that decides if a colour is "dark" then you can set a "light" text colour.

I've not personally done it myself but I've seen this used with some success:

stackoverflow.com/questions/6750695/jquery-change-text-color-based-on-containing-elements-background-color

Basically it determines if the colour is a dark one and if so it sets the text as white, otherwise it uses black.

I had some code a while ago which I wrote which altered the text color based on a background colour in a windows application by XORing the values. Can't find it now. It works for most colours. Some don't work, some look awful but do work but then it wasn't me that had to look at the colours a user had chosen for themselves.
Big MontyWeb Ninja at largeCommented:
taken from stackoverflow.com/questions/9600295/automatically-change-text-color-to-assure-readability, this may give you what you're looking for:

function invertColor(hexTripletColor) {
    var color = hexTripletColor;
    color = color.substring(1);           // remove #
    color = parseInt(color, 16);          // convert to integer
    color = 0xFFFFFF ^ color;             // invert three bytes
    color = color.toString(16);           // convert to hex
    color = ("000000" + color).slice(-6); // pad with leading zeros
    color = "#" + color;                  // prepend #
    return color;
}
$("h1")
    .css("background-color", "#FFCC00")
    .css("color", invertColor("#FFCC00"));

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brianmfallsAuthor Commented:
Thanks for the help friends.  Here's the finished product, all cleaned up, dynamically looped, and so on...

	<script type="text/javascript">
		$(document).ready( function() {
			
				function isDark(color) {
					var match = /rgb\((\d+).*?(\d+).*?(\d+)\)/.exec(color);
					return parseFloat(match[1])
						 + parseFloat(match[2])
						 + parseFloat(match[3])
						   < 3 * 256 / 2; // r+g+b should be less than half of max (3 * 256)
				}
			
				<cfoutput query="gto">

					$('###gto.containerID#').attr('bgcolor','###gto.value#');
					$('###gto.containerID#').css({
						backgroundColor: '###gto.value#'
					});
					<cfif len(gto.supportContainerID)>
						$('###gto.supportContainerID#').attr('bgcolor','###gto.value#');
						$('###gto.supportContainerID#').css({
							backgroundColor: '###gto.value#'
						});
					</cfif>
					
					var #gto.fieldID#CallbackElement = $('###gto.containerID#')
					$('###gto.fieldID#').jPicker(
						{},
						function(color, context){
							var all = color.val('all');
							var hex = color.val('hex');
							$('###gto.containerID#').attr('bgcolor',(all && '##' + all.hex));
							$('###gto.containerID#').css({
								backgroundColor: hex && '##' + hex || 'transparent'
							});
							<cfif len(gto.supportContainerID)>
								$('###gto.supportContainerID#').attr('bgcolor',(all && '##' + all.hex));
								$('###gto.supportContainerID#').css({
									backgroundColor: hex && '##' + hex || 'transparent'
								});
							</cfif>
							$('###gto.containerID#').css("color", isDark($(this).css("background-color")) ? 'white' : 'black');
							var emailID = '#session.emailID#'
							var fieldID = '#gto.fieldID#'
							$('##templateOptionBlock').load('http://#cgi.server_name#/admin/#application.module#/act/act.template.options.cfm',{'emailID': emailID, 'fieldID': fieldID, 'value': hex}, function() {
								//alert('#gto.title# Saved');
							});
						}
					);
				</cfoutput>
					
			});
	</script>

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