fillColor property
(optional) indicates both that the path marks off a polygonal area and specifies the fill color to use as an overlay within that area. The set of locations following need not be a "closed" loop; the Maps Static API server will automatically join the first and last points. Note, however, that any stroke on the exterior of the filled area will not be closed unless you specifically provide the same beginning and end location.
Implementation
final Color? fillColor;