Sure, I can help you with that! Here's how you can change the color of rows every time the value in the first column changes:

1. Select the entire range of your data, including the first column with plot numbers.
2. Click on the "Format" menu and select "Conditional Formatting".
3. In the "Conditional Formatting" dialog box, select "Formula Is" from the drop-down menu under "Condition 1".
4. In the formula bar, enter the following formula:
   Formula:

   =MOD(SUM($A$1:A1),2)=1 

5. Click on the "Format" button and choose the fill color you want to use for the highlighted rows.
6. Click "OK" to close the "Format Cells" dialog box.
7. Click "OK" again to close the "Conditional Formatting" dialog box.

What this formula does is it sums up all the values in column A from the first row to the current row, and then takes the remainder when divided by 2. If the remainder is 1, it means that the sum of all the values up to that row is odd, which indicates a new plot number. We use the MOD function to get the remainder, and the SUM function with a mixed reference ($A$1:A1) to sum up the values up to the current row.

Now, every time the plot number changes, the row will be highlighted with the color you chose.