Indication outside an defined area

[Hunter_wow]

Hi. I´m having a square diagram who got 3 dots thats connected in it
When a dot gets outside the diagram the cell for that dot is getin
red.
But now the diagrams up-left corner is cut off(pic
http://hem.bredband.net/hunter85/diagram.jpg) and I dont know how t
make the cells indicate red for that tilted area.

Get the excel file here: http://hem.bredband.net/hunter85/diagram.xls
The light-Blue area is the value that changes. Note that dot nr.2 i
not red like dot nr. 1.

(Hope u understand what I mean. My english is not what it´s supposte
to be)

Grateful Regards:

//Templa

 

[Hunter_wow]

I have heard this problem needs to be solve by macro so I really need
youre help. (know nothing about macro)