Tkinter - pixel or widget color

[pavel.kosina]

I would need to get at canvas pixel color under certain moving widget or 
better (= faster?) colors/"types" of underlying static widgets that are 
of polygon shape (not rectangle).

How to arrange it without using higher math that must have to compute 
actual distance of each of point on a polygon?

I have found find_overlapping() but its not what I need and do not found 
something like getColorPixel().

Pavel