Formula or Macro to generate alternate shading of row groupings based on changed values in last column

I am trying to generate an excel formula or macro (whichever is most appropriate) which will shade alternating blocks of worksheet rows. NOT an every other row shading format or every ‘n’ rows shading. The number of shaded rows is going to vary. I will have anywhere from 1 – 20 rows in a single grouping of either shaded or unshaded.

These worksheets represent physical furniture items donated to a non-profit charity by various donors. The donating parties sometimes give just a single item, and they sometimes give several items. Donated items are tracked individually in a spreadsheet with EACH row of that donor’s provided items designated with the donor's initials in one particular column.

At the end of the month, we generate a report of ALL items donated during that month (filtered by another column of the date range items came in). After generating that end of the month report, I want to alternatively shade the items in blocks to more easily visually represent the end of one donor’s items and the beginning of the next donor’s items. I am trying to come up with a row shading formula that triggers an alternating shade or no-shade based on whether the value in the “initials” row in the same or different as the previous row – keeping like with like.

I hope my explanation makes sense! I saved two images of an example of an original vs what I HOPE to generate. I accomplished THIS end result by manually formatting and shading the appropriate cells but want to avoid that manual step. How can I automate that process?

Original

Intended End Result