highlight irregular area

I use a parallel color image to detect when a click or a drop happens in an irregular area of a picture. This work great.
The question is, is there a way to highlight the area where the object is dropped?

Just draw over the image, FillPolygon on the Graphics object.

Sorry? . There is a map (a picture) with regions, I’ve another picture equal, not visible, with each region colored with an specific color, so when click on the real picture I get the coordinates and I get the region by color. I would like to higlight the region clicked on the main picture. Obviously, the map regions are not any regular shape.

Could you use something like this? http://forums.realsoftware.com/viewtopic.php?p=260794#p260794

It uses FloodFill with a transparent color (alpha=255) on a color coded foreground picture and then draws it on top of a background picture. The background picture shows through the transparent parts of the foreground.