Conditional formatting or formula to fill box based on date criteria

Hello,

I am putting together a spreadsheet for work which has forecast dates (F/C on doc). I want this date to then fill the applicable month and year box in the calendar part. I can't work out whether to do a formula which will fill the box and then use conditional formatting to then colour the box in.

I want to make it as automated as possible so I only need to add the forecast as these will change and other items will be added to the spreadsheet as we go on.

Thanks for your help,
Sam