some natural color mixer

mixercore.js

// Paint Colour Mixer
// copyright Stephen Chapman, 18th April 2006
// you may copy this code but please keep the copyright notice as well
var baseC = '256,256,256';
var redC = '-2,-8,-8';
var blueC = '-8,-8,-2';
var yellowC = '0,0,-8';
var orangeC = '1,1,0';
var greenC = '-4,0,-3';
var purpleC = '1,0,1';
var blackC = '-3,-4,-1';
var redV = blueV = yellowV = 0;
var totC = new Array(0, 0, 0);

function change(r, y, b) {
    totC[0] += r;
    totC[1] += y;
    totC[2] += b;
    var t = Math.max(totC[0], totC[1], totC[2]);
    if (t > 32) t = 32 / t;
    else t = 1;
    redV = Math.round(totC[0] * t);
    yellowV = Math.round(totC[1] * t);
    blueV = Math.round(totC[2] * t);
    colour();
}
function colour() {
    document.getElementById('rd4').innerHTML = totC[0] / 32;
    document.getElementById('bl4').innerHTML = totC[2] / 32;
    document.getElementById('ye4').innerHTML = totC[1] / 32;
    var shade = new mathArray(baseC);
    var tot = redV + blueV + yellowV;
    if (tot > 0) {
        var redA = new mathArray(redC);
        redA.multiply(redV * redV / tot);
        shade.add(redA);
        var blueA = new mathArray(blueC);
        blueA.multiply(blueV * blueV / tot);
        shade.add(blueA);
        var yellowA = new mathArray(yellowC);
        yellowA.multiply(yellowV * yellowV / tot);
        shade.add(yellowA);
        var orangeA = new mathArray(orangeC);
        orangeA.multiply((redV * yellowV) / 32);
        shade.add(orangeA);
        var greenA = new mathArray(greenC);
        greenA.multiply((blueV * yellowV) / 32);
        shade.add(greenA);
        var purpleA = new mathArray(purpleC);
        purpleA.multiply((blueV * redV) / 32);
        shade.add(purpleA);
        var blackA = new mathArray(blackC);
        blackA.multiply((blueV * redV * yellowV) / 1024);
        shade.add(blackA);
    }
    shade.max(255);
    shade.min(0);
    shade.int();
    document.getElementById('patch').style.backgroundColor = 'rgb(' + shade.value[0] + ',' + shade.value[1] + ',' + shade.value[2] + ')';
}
function set() {
    totC[0] = totC[1] = totC[2] = redV = yellowV = blueV = 0;
    colour();
}

utility.js

// mathArray Class
// copyright Stephen Chapman, 13th April 2006
// you may copy this code but please keep the copyright notice as well


function mathArray(vals) {
    var temp = vals.split(',');
    var len = temp.length;
    this.value = [];
    for (var i = 0; i < len; i++) {
        if (Number(temp[i]) == temp[i]) this.value.push(Number(temp[i]));
    }
}
mathArray.prototype.add = function (mA) {
    var len = Math.min(this.value.length, mA.value.length);
    for (var i = 0; i < len; i++) {
        this.value[i] += mA.value[i];
    }
};
mathArray.prototype.subtract = function (mA) {
    var len = Math.min(this.value.length, mA.value.length);
    for (var i = 0; i < len; i++) {
        this.value[i] -= mA.value[i];
    }
};
mathArray.prototype.multiply = function (num) {
    for (var i = this.value.length - 1; i >= 0; i--) {
        this.value[i] *= num;
    }
};
mathArray.prototype.replace = function (mA) {
    this.value = '';
    var len = mA.value.length;
    for (var i = 0; i < len; i++) {
        this.value[i] = mA.value[i];
    }
};
mathArray.prototype.equal = function (mA) {
    var len = mA.value.length;
    if (this.value.length != len) return false;
    for (var i = 0; i < len; i++) {
        if (this.value[i] != mA.value[i]) return false;
    }
    return true;
};
mathArray.prototype.max = function (num) {
    for (var i = this.value.length - 1; i >= 0; i--) {
        if (this.value[i] > num) this.value[i] = num;
    }
};
mathArray.prototype.min = function (num) {
    for (var i = this.value.length - 1; i >= 0; i--) {
        if (this.value[i] < num) this.value[i] = num;
    }
};
mathArray.prototype.int = function () {
    for (var i = this.value.length - 1; i >= 0; i--) {
        this.value[i] = Math.round(this.value[i]);
    }
};