Is there any way to customize the color and radius of the clustered circles?

[axelerate]

I would like to style the clusters so as to impart rules on how wide the cluster zones should be and what color pattern to abide to. EDIT: The styling should be programmatic, and not just a change to a stylesheet.

[fungiboletus]

Yes it's possible, but there is no real API for that. You have to do write some code.

Check this source code for example.