Colour conditional formatting alternating blocks of rows

Afternoon all

How do I set up an automatic colour conditional formatting for alternating blocks of rows? At present I manually colour format to highlight rows of data so that one weeks data (typically anything between 0-4) rows is different from the previous. I have a column that ascribes a number to a week of the year, but I cannot use this to do for example Pink=odds, and Yellow=evens because some weeks might not have any data (and therefore have no rows), and I am more concerned with there being a contrast between the weeks that do show.

I've attached the spreadsheet as it is so you can see how I am currently doing the manual formatting.

Any suggestions?

Dean