Compare 2 columns and highlight new items in second column - excel

Question

Situation:
I have an excel macro which imports a column of data into an existing sheet in the next free column, it also clears formatting of the previous column which will be set at the completion of the macro (the bit I'm trying to work out here).
I need the code to compare each cell in the new column to the previous column to see if there is a match, if no match then highlight the cell.
Problem:
I keep getting type mismatch errors, or the code does not run. My latest attempt (which incluces copying the unique data to a different sheet which would be a bonus if working) is below.
Dim rngCell As Range
For Each rngCell In Range(Cells(2, Worksheets("Data").Columns(LastColumn)), Cells(10000, Worksheets("Data").Columns(LastColumn)))
'I know hardcoding values is bad, but i did this for testing purposes
If WorksheetFunction.CountIf(Range(Cells(2, Worksheets("Data").Columns(LastColumn)), Cells(10000, Worksheets("Data").Columns(LastColumn))), rngCell) = 0 Then
Range("D" & Rows.Count).End(xlUp).Offset(1) = rngCell
End If
Next
Ideal outcome:
The code runs through and highlights unique values in column 1 (using column index references as each day a new column is imported).
The code copies the unique values to another sheet for ease of use.
Thanks in advance for any pointers or code.

Answer 1

Since you are only posting a part of your code, I'd have to assume that the part wher you insert and clear formatting is already working well.
Sometimes you define a worksheet, sometimes you don't so I'm not sure what sheet we are working with here.
But just to clarify, if you had data in column "A", and then ran the macro to paste data in column "B", would you want something like this:
prevCol = 1
lastCol = 2
Set Rng = Range(Cells(2, prevCol), Cells(100, prevCol))
Set Rng2 = Range(Cells(2, lastCol), Cells(100, lastCol))
For Each rngCell In Rng
If WorksheetFunction.CountIf(Rng2, rngCell) = 0 Then
rngCell.Interior.Color = RGB(250, 230, 20)
End If
Next
Where unique items in the column that existed before the new one got inserted are highligted?
So in the end, maybe something more like this:
Sub SubName()
Dim sht As Worksheet
Dim lastCol As Long, lastRow As Long
Set sht = Worksheets("Data") 'or whatever
' Instert column
' clear formatting
lastCol = sht.Cells(2, sht.Columns.Count).End(xlToLeft).Column
lastRow = sht.Cells(sht.Rows.Count, lastCol - 1).End(xlUp).Row
For Each rngCell In Range(Cells(2, lastCol - 1), Cells(lastRow, lastCol - 1))
If WorksheetFunction.CountIf(Range(Cells(2, lastCol), Cells(lastRow, lastCol)), rngCell) = 0 Then
rngCell.Interior.Color = RGB(250, 230, 20)
End If
Next
End Sub