Lighten, Darken, or Otherwise Modify Colors

modifyColor.js

// grok'd from TinyColor
// https://bgrins.github.io/TinyColor/

    toString: function(format) {
        var formatSet = !!format;
        format = format || this._format;

        var formattedString = false;

_applyModification: function(fn, args) {
        var color = fn.apply(null, [this].concat([].slice.call(args)));
        this._r = color._r;
        this._g = color._g;
        this._b = color._b;
        this.setAlpha(color._a);
        return this;
    },
    lighten: function() {
        return this._applyModification(lighten, arguments);
    },
    brighten: function() {
        return this._applyModification(brighten, arguments);
    },
    darken: function() {
        return this._applyModification(darken, arguments);
    },
    desaturate: function() {
        return this._applyModification(desaturate, arguments);
    },
    saturate: function() {
        return this._applyModification(saturate, arguments);
    },
    greyscale: function() {
        return this._applyModification(greyscale, arguments);
    },
    spin: function() {
        return this._applyModification(spin, arguments);
    }     
}

function desaturate(color, amount) {
    amount = (amount === 0) ? 0 : (amount || 10);
    var hsl = tinycolor(color).toHsl();
    hsl.s -= amount / 100;
    hsl.s = clamp01(hsl.s);
    return tinycolor(hsl);
}

function saturate(color, amount) {
    amount = (amount === 0) ? 0 : (amount || 10);
    var hsl = tinycolor(color).toHsl();
    hsl.s += amount / 100;
    hsl.s = clamp01(hsl.s);
    return tinycolor(hsl);
}

function greyscale(color) {
    return tinycolor(color).desaturate(100);
}

function lighten (color, amount) {
    amount = (amount === 0) ? 0 : (amount || 10);
    var hsl = tinycolor(color).toHsl();
    hsl.l += amount / 100;
    hsl.l = clamp01(hsl.l);
    return tinycolor(hsl);
}

function brighten(color, amount) {
    amount = (amount === 0) ? 0 : (amount || 10);
    var rgb = tinycolor(color).toRgb();
    rgb.r = mathMax(0, mathMin(255, rgb.r - mathRound(255 * - (amount / 100))));
    rgb.g = mathMax(0, mathMin(255, rgb.g - mathRound(255 * - (amount / 100))));
    rgb.b = mathMax(0, mathMin(255, rgb.b - mathRound(255 * - (amount / 100))));
    return tinycolor(rgb);
}

function darken (color, amount) {
    amount = (amount === 0) ? 0 : (amount || 10);
    var hsl = tinycolor(color).toHsl();
    hsl.l -= amount / 100;
    hsl.l = clamp01(hsl.l);
    return tinycolor(hsl);
}

// Spin takes a positive or negative amount within [-360, 360] indicating the change of hue. 
// Values outside of this range will be wrapped into this range.

function spin(color, amount) {
    var hsl = tinycolor(color).toHsl();
    var hue = (hsl.h + amount) % 360;
    hsl.h = hue < 0 ? 360 + hue : hue;
    return tinycolor(hsl);
}