Dual pane diff, hide common lines

one.txt     two.txt

a           d
b           e
c           f
d           g
e           h
f           i

diff -y --suppress-common-lines one.txt two.txt

a  < # I'd expect this to be >
b  <
c  <
>  g
>  h
>  i

# The other way?

diff -y --suppress-common-lines two.txt one.txt
    
   >  a # really?
   >  b
   >  c
g  <
h  <
i  <

-1              suppress column 1 (lines unique to FILE1)
-2              suppress column 2 (lines unique to FILE2)
-3              suppress column 3 (lines that appear in both files)

comm -3 one.txt two.txt

a
b
c
        g
        h
        i