I've got a Google map that allows you to enter your postcode and shows results within a certain radius of that point - a very common application of the API.

I have it plotting a circle to represent the area covered (easy enough), but I'd like to "grey out" the map (e.g. by applying a semi-transparent layer over it) except for the area within the circle, which shows the map as normal.

I haven't found anything like this anywhere - is it even possible?

Many thanks for reading this!