我的版本:

function RandomColor() {
  var hex = (Math.round(Math.random()*0xffffff)).toString(16);
  while (hex.length < 6) hex = "0" + hex;
  return hex;
}

function get_random_color() {
    return "#" + (Math.round(Math.random() * 0XFFFFFF)).toString(16);
}

http://jsfiddle.net/XmqDz/1/

一个简短的答案，有精确大小的填充:

'#' + ((1<<24)*(Math.random()+1)|0).toString(16).substr(1)

function randomColor(format = 'hex') {
    const rnd = Math.random().toString(16).slice(-6);
    if (format === 'hex') {
        return '#' + rnd;
    }
    if (format === 'rgb') {
        const [r, g, b] = rnd.match(/.{2}/g).map(c=>parseInt(c, 16));
        return `rgb(${r}, ${g}, ${b})`;
    }
}

下面是@Anatoliy提供的解决方案。

我只需要生成浅色(作为背景)，所以我使用了三个字母(#AAA)格式:

function get_random_color() {
    var letters = 'ABCDE'.split('');
    var color = '#';
    for (var i=0; i<3; i++ ) {
        color += letters[Math.floor(Math.random() * letters.length)];
    }
    return color;
}

Use:

function random_color(format)
{
    var rint = Math.round(0xffffff * Math.random());
    switch(format)
    {
        case 'hex':
            return ('#0' + rint.toString(16)).replace(/^#0([0-9a-f]{6})$/i, '#$1');
            break;

        case 'rgb':
            return 'rgb(' + (rint >> 16) + ',' + (rint >> 8 & 255) + ',' + (rint & 255) + ')';
            break;

        default:
            return rint;
            break;
    }
}

升级版:

function random_color( format ){
  var rint = Math.floor( 0x100000000 * Math.random());
  switch( format ){
    case 'hex':
      return '#' + ('00000'   + rint.toString(16)).slice(-6).toUpperCase();
    case 'hexa':
      return '#' + ('0000000' + rint.toString(16)).slice(-8).toUpperCase();
    case 'rgb':
      return 'rgb('  + (rint & 255) + ',' + (rint >> 8 & 255) + ',' + (rint >> 16 & 255) + ')';
    case 'rgba':
      return 'rgba(' + (rint & 255) + ',' + (rint >> 8 & 255) + ',' + (rint >> 16 & 255) + ',' + (rint >> 24 & 255)/255 + ')';
    default:
      return rint;
  }
}