Diamond Day is played on two guitars. One guitar repeats a figure the entire song, 
whilst the other joins in at times playing two short chords.
This song actually works best with a Capo on 2.

Here is the main figure, repeated throughout on one guitar:

CAPO 2

e|---------------------------------------------------------|
B|---1-----------------------------------------------------|
G|-2---0-2-0---0-------------------------------------------|
D|-----------2---0-2-0-----------------0-------------------|
A|---------------------3---0-3-0-----3---------------------|
E|-------------------------------3-------------------------|



The other guitar harmonizes with the first (listen for timing) by alternating between 
two chords.
This one is tricky to figure out, but here's my best guess (relative to capo on 2 
again). Try upstroking them:

   D  & F#m
e|----------|
B|-1--------|
G|-0----0---|
D|-2----2---|
A|-3----2---|
E|----------|

Such a lovely song. Looks like Vashti likes to play it down a half-step with the capo on 
1 (same relative fingerings) live these days.
This is one of my first tabs; if anyone has any ideas on the chord harmonies, or 
anything else, please drop a comment or reach me at jkhillery@gmail.com
Enjoy!