From https://developers.google.com/kml/documentation/kmlreference
```
The opacity of a color comes from the alpha component of <color> and is never randomized.
```

You should move change this to 
```
var color = Color.fromRandom(options);
color.alpha = parseInt(value.substring(0,2), 16) / 255.0;
```
and get rid of the `options.alpha` line.

I think ultimately I'm going to want to change the implementation of `Color.fromRandom` some more to better suite general purpose needs, but at first glance it looks like you coded it exactly how KML specified (except for the one item above), and I'd that's all we need for now.  Nice work.