I need a function which returns only dark colors.

I am able to get random colors using below code. But how to limit this to fetch only dark colors.

```js
document.getElementById('mydiv').style.backgroundColor = '#' + Math.floor(Math.random() * 16777215).toString(16);
```

```css
div {
  height: 100px;
  width: 100%;
}
```

```html
<div id="mydiv"></div>
```

If not how can I define some pool of colors in an array and fetch from that ?