It's only one column ....so in the example above, that would be Column D. If that column had the "IP" text value (again in the example above...that would be D2 and D4) the cell(s) directly above it is highlighted (so this would be D1 and D3). That's all. No other columns are being referenced for the highlight action.
OK, so when you say "unique", you mean that there is only one "different" value showing in column D, though it that value may show up many times?
So, then would an example of not unique be something like where "IP" appears on one line, and "DQ" appears on another line (even if they both only appear once)?
It would be best to just pick some large row number that you will never hit, as there are a few problems using the whole column, i.e.
- you would be doing unnecessary calculations on tons of rows which could slow things down
- the formula looks at one cell below the current row, so on the last row, it would be looking off the sheet, which would cause an error
So, if you choose some row number you will never hit, it should work, selecting D2 down to that row number, i.e.