Placing a box or shaded area on a variable chart

[xenoborg4]

The position of all the lines changes relative do the data in the workbook.
Using arrays, I can find the point where yellow = black.

So, I can find the cords of where I want a box and put them in cells. The question is how do I tell it to make a box on my chart.

 

[PaddyD]

I'm not clear about what you actually want here. Rather than the generic 'I can find the point where yellow = black' and 'I can find the cords of where I want a box and put them in cells', be precise - given the data, what, exactly, do you need - do you need, perhaps, to set a different background for the area between two curves?