More than 3 conditional formats in Excel

Trouble is that macros seem to be only activated when cell values are changed. All of the values I am working with are already entered into the spreadsheet. The only way to activate the color change is to reenter the value one cell at a time, which would take way too long seeing as there are over 1000 cells per section, and up to 10 or so sections...

In that case, take aquarelle macro and rename the method to some thing else. Lets say it is ConditionalFormatAfterTheFact. Also remove the reference to passed variables.

So now you should have

Private Sub ConditionalFormatAfterTheFact() 
... 
End Sub

The second change you need to make is change this

Set MyPlage = Range("R7:R1000")

MyPlage refered to the range where to color was to be applied. You change it to your requirement as for example

Set MyPlage = Range("A7:F56")

Now to Run this modifed macro. Of course you need to modify the conditions. Personally I am not a big fan of a lot of IFs

So instead of

        If Cell.Value = "Extreme" Then 
            Cell.Interior.ColorIndex = 3 
        End If 
        If Cell.Value = "Hight" Then 
            Cell.Interior.ColorIndex = 4 
        End If 

        If Cell.Value <> "Extreme" And Cell.Value <> "Hight" And Cell.Value <> "Medium" And Cell.Value <> "Low" Then 
            Cell.Interior.ColorIndex = xlNone 
        End If

you can have

    Select Case Cell.Value 
     
        Case = "Extreme" 
            Cell.Interior.ColorIndex = 3 
         
        Case = "Hight" 
            Cell.Interior.ColorIndex = 4 
         
        Case Else 
            Cell.Interior.ColorIndex = xlNone 
    End Select

I entered this exactly:

Private Sub ConditionalFormatAfterTheFact()
Set MyPlage = Range("C2:C8381")
For Each Cell In MyPlage

Select Case Target

Case 106576 To 154925
Cell.Interior.ColorIndex = 46

Case 235523 To 241668
Cell.Interior.ColorIndex = 46

Case 368764 To 397255
Cell.Interior.ColorIndex = 46

Case 413751 To 419523
Cell.Interior.ColorIndex = 46

Case 495867 To 519225
Cell.Interior.ColorIndex = 46

Case Else
Cell.Interior.ColorIndex = xlNone
End Select

Next
End Sub

and it did not work. What did I do wrong?

I am presuming that you did run the macro. Here is one issue
Select Case Target

There is no "Target". There is "Cell"

Select Case Cell.Value

OK, that worked. Thank you very much.