Highlight Duplicated With Alternating Colors

I have a spreadsheet that contains thousands of rows and I need to highlight all the duplicates in Column B.

What I need though is one group o duplicates to be colored one color and then the next group of duplicates be colored a different color. I need just a 2 color banding.

My need for 2 colors is that the cells contain 9 digit numbers and there can be duplicate groups right next to each other and for the eye to distinguish a different grouping of cells I need that 2 color banding.

I have the below code that colors everything in one color. Can I be modified or a completely new code to do 2 colors?

Code:
Sub Dups()
Dim Rng As Range
Dim CL As Range

Set Rng = Range(Range("B1"), Range("B" & Rows.Count).End(xlUp))

For Each CL In Rng
If WorksheetFunction.CountIf(Rng, CL.Value) > 1 Then
CL.Interior.ColorIndex = 6
End If
Next CL
End Sub