From selected cell, choose a range

I'm getting hung up on syntax, so am asking for help. I have the following variables:

Dim FirstCol As Long
    Dim LastCol As Long

FirstCol is my selected column, which can be anywhere on the page, OR FirstCol is Column A (choice is up to the user)
LastCol is the last populated column on the activesheet
In my selected column, I'm stepping down through the cells to determine which cells are duplicates, to color those with alternating bands of color. My code below works great for the selected column, but I want to color the range from FirstCol to LastCol within the rows currently selected by the macro, and can't figure out how to phrase that. Your help is greatly appreciated.

TC = 1
    For row = TopCell To LastCell
        If TC = 1 Then
            Color = TxtColor1
        Else
            Color = TxtColor2
        End If
        
        If Cells(row, Selection.Column).Value = Cells(row + 1, Selection.Column).Value Then
            Selection.Resize(Selection.Cells.Count + 1).Select
        Else
            If Selection.Cells.Count > 1 Then
                Selection.Interior.Color = Color
                Cells(row + 1, Selection.Column).Select
                TC = TC + 1
        If TC = 3 Then TC = 1
            Else
                Cells(row + 1, Selection.Column).Select
            End If
        End If
        
    Next row