Convert field of values to colorful polygon

Say I have a data structure like List[Tuple[GPSPoint, Value]] whose gps points can all be bounded by some polygon. How can I render a polygon with those values mapped to a particular color? I can work with any data structure. The only requirement is to take some field of values between 1 and 0 and map those values to colors.
This comes close:

But is applied to the whole globe and is still taking a bunch of rules and passing that to a function that knows how to convert those rules to colorful elevation bands.