How do I color 3 rows at the same time using 'Open' in Apple Numbers?

To highlight an entire row using Conditional Highlighting you can do something like this.

Add an extra "helper" column, which you can later hide, with a formula like this:

The formula in D2, filled down:

=IF(C2="Open","","~")

If your region uses ; as the decimal separator use this instead:

=IF(C2="Open";"";"~")

Then select all the body cells in columns A through C (in my example: A2:C10) and apply a Conditional Highlighting rule like this:

To get that $D2 first click the box-and-arrow icon then click cell D2 in the table. Be sure to select the $ Preserve Column anchor.

SG