Excel: Count cells with specific value + colour

Hi there, 

I would like to be able to count the number of cells that contain a specific value and are shaded a specific colour. This is for a rota spreadsheet that will be tallying the total number of shifts which have been agreed. The cells that contain "Yes" as a value from a drop down list and are shaded green, should be counted as part of the quarterly total. 

I'm assuming that a VBA custom function would be needed for this. I've tried a few but cannot figure out a way to get this to work with both a specific value and colour. I would be very grateful for anyone that is able crack this challenge. 

In the example screenshots, it is the cells shaded in green that would need to be counted and the totals appear in column GJ.

Best regards, 

Daniel