Late to the party, hope this helps you :)
Assuming the data set...
[attach=1]
Push the big button.
[attach=2]
Alternating rows are highlighted
[attach=3]
VBA code:
Option Explicit
'Settings
Const FIRST_COL As String = "A"
Const prev_COL As String = "F"
Sub main()
'Define colour array
Dim colour(1) As Variant
Dim colour_flag As Byte
'Define the colour in RGB here
'255,255,255 = white. Experiment with different values.
colour(0) = RGB(255, 255, 255)
colour(1) = RGB(111, 222, 255)
colour_flag = 1
Dim current_col1_val, current_col2_val As String
Dim prev_col1_val As String
Dim row As Long
Dim highlight_first_row, highlight_prev_row As Long
'Activate sheet
Sheets("Data").Activate
'Start row
row = 2
highlight_first_row = 2
highlight_prev_row = 2
'Get values
current_col1_val = Range("A" & row).Value
current_col2_val = Range("B" & row).Value
prev_col1_val = current_col1_val
'Loop until last row
While current_col2_val <> ""
'If current data in column A is different from previous row, AND previous data is empty then...
If (current_col1_val <> prev_col1_val And prev_col1_val = "") Then
'Switch colour
colour_flag = colour_flag Xor 1
Call Highlight(highlight_first_row, row - 1, colour(colour_flag))
'Make current row the new start row for next set of highlights
highlight_first_row = row
End If
'Save current data in column A
prev_col1_val = current_col1_val
'Move onto next row
row = row + 1
current_col1_val = Range("A" & row).Value
current_col2_val = Range("B" & row).Value
Wend
colour_flag = colour_flag Xor 1
Call Highlight(highlight_first_row, row - 1, colour(colour_flag))
End Sub
'Highlight cells
Sub Highlight(ByVal first_row As Long, ByVal prev_row As Long, ByVal colour As Variant)
Range(FIRST_COL & first_row & ":" & prev_COL & prev_row).Interior.color = colour
End Sub
How to add VBA to Excel: https://www.ablebits.com/office-addins-blog/2013/12/06/add-run-vba-macro-excel/ (https://www.ablebits.com/office-addins-blog/2013/12/06/add-run-vba-macro-excel/)