I have a spreadsheet with about 4000 lines of data. The lines are grouped by
an unique identifier. One unique identifier has several lines that go with
it. I wanted to use a conditional format to highlight every other group of
data. For example:

1
1
2
2
3
3

Is there a way to highlight both of the 1's and skip the 2's and then
highlight the 3's or is this just a task to do by hand?