It depends on the cat. I've had two calicos and neither flipped out. Both
did/do their share of PMSing but so did Tigger and she was a tabby. In my
experience it has been the torties that have been unpredictable

W

My first cat I had when I was 8 years old was a calico.  She was born to the
next door neighbor cat the day our dog died.  They called her Blondie, and I
kept the name, even though she was white with apricot and gray patches.
Blondie liked me to carry her draped over my shoulders.  I dressed her in
doll clothes and pushed her around in a doll carriage.  When I climbed the
apple trees in our yard, she was right there with me.  When the tomboy in me
hunted gartner snakes, the cat went, too and helped me find them.
My mother did not allow pets in the house, but I snuck Blondie in the
bedroom window until she ratted on me by asking my mother to let her in when
I was at school and my mother was in my room.
I had to leave Blondie behind with a neighbor when my dad got transferred to
an area with high traffic.  My parents told me she would be much better off
and safer in her familiar territory.  I kept in touch with her through the
neighbor boy, who wrote me and always put a muddy kitty pawprint by the
signature.
Blondie lived a good life until I was through college and married.  She died
in her sleep under her favorite bush.
The mother of the family that took Blondie told me much later that having
Blondie was the best thing for her kids.  The girls dressed her in doll
clothes and pushed her around in a doll buggy, just like I did.
Many years after Blondie died, and I was married with almost grown children,
somebody dumped an adolescent calico kitten in our neighborhood.  She had
the same half apricot and half gray nose that my beloved Blondie had.  Both
our resident cats and our dog insisted we keep her, and, of course, I
agreed.  I called her Moxie.
We lived in a semi-rural area with a couple of acres and a barn.  Each
evening about 7 p.m., Mac, one of our old male cats would come by the house
as if picking up a date.  Moxie would go into the pasture and down to the
barn with him.  Each evening at 9 p.m., Mac would bring her back to the
house.  It was so sweet.
My husband got transferred and we drove with the three cats from the
Northwest U.S. to Texas. (Our dog had died of congestive heart failure.)
During the trip, Moxie was the cheerleader for Mac and Josh.  As soon as we
opened the crates in the motel room, she'd roust them out to explore.
When we were getting ready to leave to continue our trip, she would go into
Josh's crate and use his litter box.
Moxie was Josh's nurse when he developed diabetes.  I think she helped him
live longer than he would have lived otherwise.
We could do anything with Moxie.  She loved to be combed.  She didn't mind
having her claws clipped.  When she had to have an ultrasound, she did not
complain when her tummy was shaved and lay calmly on her back on the table
during the whole procedure.
When Blondie died, I mourned her a long, long time.  Now, there is another
hole in my heart for Moxie.
These are my experience with calico cats.
Maybe I just got lucky.  Maybe what you hear is an urban legend.
Annie

I don't know that I'd call the calicos that I've had "unstable". They
all were cantancerous<SP?> and at times moody. From time to time they
could even be a bit on the nasty side to other cats.

Dunno, Brian. I've always had the opinion that coat color didn't
determine personality in any way.
However, I do have two orange boys who are just big lazy love sucks,
holding true to *their* reputation.
I have one calico longhair. She is extremely timid, a loner, doesn't
mingle with the other cats at all. *Never* goes outside--she even used
to be terrified of open windows. She truly would be happier as an only
cat who had a lap to lay on all day. However, in a household of 5 cats,
I don't see being an only cat in her future.

Sherry

I have a 6.5lb calico (She looks black but when you get bright light on
her, she's got the calico pattern.) named Emily that is a bitch that has
a house to run.

She picks on both the male cats with a vengeance. But she's a sweet
little cat with her humans though we do get some of the attitude on
occasion.

Well, I've been around two calicos...  One was just as sweet as the day
was long, she never got mad, she nursed a puppy (and her full grown tom
cat when she had her second litter - she was fixed after that), she let
everyone "drag" her around.  Just super mellow.

Then there's Pretty Face, a visitor I have at my home.  She can be very
sweet, but she's got a mean streak (or a crazy one) a mile wide, and
for no apparent reason.  Since she isn't my cat (except for scritches),
I can't say what she's like all the time, but she is a bit nuts.

I hold the belief that grey cats are mentally impaired.  They don't
function like other cats.  They tend to be more jumpy/twitchy than
other cats.  Tuppence (RB) would just go wild, and not "zoomies" per
se, she'd run into things (like walls and doors) during her "wild"
phases (vet never found any reason for it, just said she didn't notice
things when she was excited).  I hadn't noticed it until someone at
work mentioned (on seeing a picture of my Tuppence) that all grey cats
were brain damaged or nuts.

Thinking back, I think she was right.  Tuppence was never "normal" even
for a cat, nor was any other grey I've ever been owned by.  Loved them
all though, idiosyncrasies (sp?) and all.

Smokie Darling (Annie)