How to divide a polar grid into individual sections in order to make them different colors

I need to make a cycle calendar like the birthday calendars people draw in bullet journals, so I made a polar grid with 12 concentric dividers and a black stroke. I only need the 12 segments on the outer ring of the circle (for the months of the year), as I'll be filling the center with just a white ellipse or omitting the other sections entirely.

How do I split each of the segments into its own section? That way I can fill each with a different color for each month.

Thanks!