Reverse Page Font & Background Colors

reverse-colors.js

    function invertColor(color){
        var r,g,b;
        if(color.indexOf('rgb') >= 0){
            if(color == 'rgba(0, 0, 0, 0)'){
                color = 'rgb(255,255,255)';
            }
            color = color.substring(color.indexOf('(')+1, color.indexOf(')')).split(',');
            r = color[0];
            g = color[1];
            b = color[2];

        }else{
            if(color.length != 6) {
                r = color.charAt(0);
                r = r+r;
                g = color.charAt(1);
                g = g+g;
                b = color.charAt(2);
                b = b+b;
            }else{
                r = color.substring(0,2);
                g = color.substring(2,4);
                b = color.substring(4,6);
            }
            r = parseInt(r,16);
            g = parseInt(g,16);
            b = parseInt(b,16);
        }

        r2 = 255 - r;
        g2 = 255 - g;
        b2 = 255 - b;
        return 'rgb('+r2+','+g2+','+b2+')';
    }

    function getStyle(oElm, prop){
        var strValue = "";
        if(document.defaultView && document.defaultView.getComputedStyle){
            strValue = document.defaultView.getComputedStyle(oElm, "").getPropertyValue(prop);
        }
        else if(oElm.currentStyle){
            prop = prop.replace(/\-(\w)/g, function (strMatch, p1){
                return p1.toUpperCase();
            });
            strValue = oElm.currentStyle[prop];
        }
        return strValue;
    }

    function invertElementColors(el){
        var fontColor = getStyle(el, 'color');
        var bgColor = getStyle(el, 'background-color');
        
        newFontColor = invertColor(fontColor);
        newBgColor = invertColor(bgColor);
        
        el.style.color = newFontColor;
        el.style['background-color'] = newBgColor;

    }
    function traverseReverse(el) {
        if(el.nodeType == 1){
            for(var child = el.lastChild; child; child = child.previousSibling) {
                traverseReverse(child);
            }
            invertElementColors(el);
        }
    }
    traverseReverse(document.getElementsByTagName("body")[0]);

gist!