Hi Vasean,
In Numbers, conditional highlighting can be applied only to an individual cell, and the rule controlling the highlighting must compare the value in that cell with a fixed value of with the value in another cell. A long-standing technique for the type of highlighting you want is to create a second table whose rows match the main table in height, with a single column whose width matches the width of the main table.
Cells on this table contain a formula that references the value in one of the cells on the same row of the main table, and return a value used to trigger (or not trigger) the highlighting rule.
Here's an example, using the table in my previous post.
The original table on the left, and the 'format' table on the right.
The 'format' table has had part of its 'custom formatting applied—a 240-240-240 coloured fill in the cell. The full format uses the same RGB values for the conditional colour of the text ( "yes" ). The 'format' was created by adding a column to the right side of the main table, then dragging that column away up and right until it split from the original table. The full column was then selected and the cell fill set to No fill. Then the rule described below was set for cells in rows 2 through the end of the table.

Conditional Highlighting rule for above:

To produce the effect wanted, these changes were made.
The 'format table was widened to match the width of the main table.
The custom format used for highlight was revised to include the text. making it the same grey as the fill.
The format table was moved back (Arrange > Send backward), and slid behind the main table.
The format table was locked in position (Arrange > Lock)
Result:

I have added a formula to column A, starting in row 3, and filled down to the end of the table (row 33, allowing for a full month of dates in any month).
A3: A2+1
Fill down.
The initial date (Feb 1 above) is entered in A2. The rest are filled in automatically, and the weekend dates automatically receive the apparent formatting, as seen below:

Regards,
Barry