Random Background & eye-friendly Fore-color generation

random-colors.js

function shadeColor2(color, percent, hash) {   
    var f=parseInt((hash? color.slice(1) : color),16),
        t=percent<0?0:255,
        p=percent<0?percent*-1:percent,
        R=f>>16,
        G=f>>8&0x00FF,
        B=f&0x0000FF;
    
    return  (0x1000000
                +(Math.round((t-R)*p)+R)*0x10000
                +(Math.round((t-G)*p)+G)*0x100
                +(Math.round((t-B)*p)+B))
    .toString(16)
    .slice(1);
}

function getRandomColor(hash) {
    var letters = '0123456789ABCDEF'.split('');
    var color = '';
    for (var i = 0; i < 6; i++) {
        color += letters[Math.floor(Math.random() * 16)];
    }
    
    var l = getLuminance(color);
    if(l > 90){
        //console.log("shading: " + color);
        color = shadeColor2(color, -0.25);
    }
    
    return (hash ? '#' : '') + color;
}

function invertColor(hexTripletColor, hash) {
    var color = hexTripletColor, rgb;
    if (hash) {
        color = color.substring(1);           // remove #
    } 
    color = rgb = parseInt(color, 16);          // convert to integer 
    color = 0xFFFFFF ^ color;             // invert three bytes
    
    //console.log("BG: " + getLuminance(rgb));
    //console.log("TXT: " + getLuminance(color));
    
    var lr = getLuminance(rgb);
    var lt = getLuminance(color);
    var ma = (lr - lt);
    console.log("ma: " + ma);
    if(ma < -20){
        //console.log("shading txt: " + color);
        color = shadeColor2(color, -1);
    }else if(ma < -60){
        //console.log("shading txt: " + color);
        color = shadeColor2(color, -0.5);
    }else if(ma > 7){
        //console.log("shading txt: " + color);
        color = shadeColor2(color, 1);
    }

    
    color = color.toString(16);           // convert to hex
    color = ("000000" + color).slice(-6); // pad with leading zeros
    color = (hash ? "#" : '') + color;                  // prepend #
    return color;
}

function getLuminance(rgb){ 
    rgb = parseInt(rgb, 16);
    // check for brightness or original color
    var r = (rgb >> 16) & 0xff;  // extract red
    var g = (rgb >>  8) & 0xff;  // extract green
    var b = (rgb >>  0) & 0xff;  // extract blue
    
    var luma = 0.2126 * r + 0.7152 * g + 0.0722 * b; // per ITU-R BT.709
      
    return luma;
}

// usage
var bg  = getRandomColor(true); // true implies we need the # in returned color code
$("#bg .lbl").text(bg);
$("#bg").css('background-color', bg);
var ibg  = invertColor(bg, true); // true implies we need the # in returned color code
$("#text").css('color', ibg);
$("#text .lbl").text(ibg);