How/Where do I get the color index?
I used the names of the colors: 

    For i = 1 To grpnr
        Select Case D1(i)
        Case Cells.Interior("Light Orange")
            grpsize(i) = 6
        Case Cells.Interior("Aqua")
            grpsize(i) = 4
        Case Cells.Interior("Plum")
            grpsize(i) = 3
        Case Cells.Interior("Rose")
            grpsize(i) = 2
        Case Else
            MsgBox "error in grouping color"
        End Select
    Next i
only to return error.