I've implemented my suggestion and will send it to you if you send me
an e-mail. The CF is not exactly straightforward, as you need to use
all three conditions to get the color with and without the weekly
dividing line and then the dividing line on its own. It is also
possible to implement it so that it runs like molasses in January in
Butte, Montana, but there is an easy fix to eliminate the inefficiency.

Reply direct and I will send you the spreadsheet.

Regards

Declan O'R