gradient Colors

var parseColor = function (hexStr) {
    return hexStr.length === 4 ? tr.substr(hexS1).split('').map(function (s) {
        return 0x11 * parseInt(s, 16);
    }) : [hexStr.substr(1, 2), hexStr.substr(3, 2), hexStr.substr(5, 2)].map(function (s) {
        return parseInt(s, 16);
    })
};

// zero-pad 1 digit to 2
var pad = function (s) {
    return (s.length === 1) ? '0' + s : s;
};

/*
            start     
            end     
            steps        
            gamma          （  ）
        */


var gradientColors = function (start, end, steps, gamma) {
    var i, j, ms, me, output = [],
        so = [];
    gamma = gamma || 1;
    var normalize = function (channel) {
        return Math.pow(channel / 255, gamma);
    };
    start = parseColor(start).map(normalize);
    end = parseColor(end).map(normalize);
    for (i = 0; i < steps; i++) {
        ms = i / (steps - 1);
        me = 1 - ms;
        for (j = 0; j < 3; j++) {
            so[j] = pad(Math.round(Math.pow(start[j] * me + end[j] * ms, 1 / gamma) * 255).toString(16));
        }
        output.push('#' + so.join(''));
    }
    return output;
};