Flips text color based on background luminosity

BGColor.js

HTMLElement.prototype.setBgColor = function(r,g,b){
	var el = this;
	var generateLuminance = function(r,g,b){
		return (0.299*r)+(0.587*g)+(0.114*b);
	}
	el.style.backgroundColor = 'rgb('+r+','+g+','+b+')';
	if(generateLuminance > 138){
		el.style.color = 'rgb(0,0,0)';
	}
	else{
		el.style.color = 'rgb(255,255,255)';
	}
}