About WhatColor ...

Usefull (I hope, it was my purpose) to avoid tries about right 
color if it already exists on screen. Idea from Magnify and 
Locate applications.

NB:
- No refresh when cursor is inside window, avoid feedback 
of displayed image.

- adjust position with arrow keys when mouse isnt moving.

- due to in screen constraint, displayed coordinates arent 
cursor coordinates near screen boundaries.

