Linear interpolation for hexadecimal colors.

lerp-color.js

/**
 * A linear interpolator for hexadecimal colors
 * @param {String} a
 * @param {String} b
 * @param {Number} amount
 * @example
 * // returns #7F7F7F
 * lerpColor('#000000', '#ffffff', 0.5)
 * @returns {String}
 */
function lerpColor(a, b, amount) { 

    var ah = parseInt(a.replace(/#/g, ''), 16),
        ar = ah >> 16, ag = ah >> 8 & 0xff, ab = ah & 0xff,
        bh = parseInt(b.replace(/#/g, ''), 16),
        br = bh >> 16, bg = bh >> 8 & 0xff, bb = bh & 0xff,
        rr = ar + amount * (br - ar),
        rg = ag + amount * (bg - ag),
        rb = ab + amount * (bb - ab);

    return '#' + ((1 << 24) + (rr << 16) + (rg << 8) + rb | 0).toString(16).slice(1);
}

Yeah is the string parsing necessary? I mean, it's not like I've seen a performance problem. Anyways, here's a version that just deals with hex literals: https://gist.github.com/nikolas/b0cce2261f1382159b507dd492e1ceef