Thanks DBY! I am almost there, but there is a remaining problem:
I formatted the column to have "No" background and White fonts.
I then applied the first suggestions and set =COUNTIF($C$17:$C17,$C18)=1 to apply to all values in the column.
This sets the first instance of the name to have grey background and black fonts which is what I wanted.
However the formula it also hides the names that occur only once. I don't want that!
They should have the same formatting as the other headers, even if they only occur once.
I can't figure out how to prevent that, or construct a Conditional format that sets these names back to the formatting I want.
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