Highlight Cell When Value Changes, Reset On Re-Open

[Evernight2021]

I have a column of dates (N) in date format (MM/DD/YYY), another column that counts total years worked (M), and a column with starting date (D) also in (MM/DD/YYY) format.

I'm trying to get it so that when today's date is equal to or beyond the date in column N, the years worked (M) gets incremented and then highlighted in red to make the change easy to pick out. I'm also wondering if it's possible to make it so that the next time the workbook is opened, the red cells are either changed to green or back to white and then any new column M changes would then be highlighted in red to make the new changes easy to pick out. The user would save the workbook to keep the changes to the dates after use.[TABLE="width: 990"]
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[Evernight2021]

I was able to calculate the years by applying the following formula to the cells in the M colum:

[FONT=Verdana]=DATEDIF(D12,TODAY(),"y")[/FONT]

I set the sheet to change colors of cells with value changes using:

[FONT=Verdana]Private Sub Worksheet_Change(ByVal Target As Range)
Target.Interior.ColorIndex = 3
End Sub[/FONT]

Is there a way to apply that just to the 'M' column?

I created a button to remove the colors for next use with:

[FONT=Verdana]Private Sub CommandButton3_Click()
    With ActiveSheet
        Cells.Interior.ColorIndex = xlNone
    End With
End Sub[/FONT]

Individually, all of these work fine. However, if I add a new start date of 1/1/2018 and anniversary date of 1/1/2019 for example, set my computer date to 1/1/2019, and open the workbook, the cell in column M (years) will increment properly, however the cell doesn't change color. It does change color if I manually make the changes. Is there something I'm missing in order to get the color change to work?