At least over here (US).  The other year I was given the opportunity to
drive an RNLI 47 foot motor lifeboat in the UK.  I was just following
the boat commander's instructions, but I soon noticed that the channels
were all marked "backwards."  We were following a freighter out of a bay
and all the red nav markers were on the right.  There's no excuse for my
not already knowing this, but it wasn't until I queried the friend who'd
arranged the ride with the RNLI that I learned the world is divided into
several areas, and the navigation marker positioning is opposite in some
of the areas.  He didn't know WHY it was this way, but that's the way it
is.....

C. Marin Faure
GB36-403 "La Perouse"
Bellingham, Washington

Marin said:

You're right Marin
The Red to Port and Green to Starboard is the IALA standard
The IALA has two buoyage systems...A&B.
Broadly,'A' is for the world excluding most of north and south America.
'B' is for North and south America and some of Asia.
'A' has Red buoys to Port entering harbour, 'B' has the reverse.
It's all made clear at http://www.beta.ialahq.org/pages/english/p4/p4b.htm.
I have borrowed the following from http://www.navis.gr/marinav/buoy.htm

BUOYAGE
Attempts to establish an international uniform system of buoyage have never
met with success. A system proposed in 1936 under the auspices of the League
of Nations might have succeeded had not World War II intervened before a
sufficient number of maritime States had ratified the system. The buoyage
system adopted for British waters was based on the 1936 proposals. The
system called the 'lateral system' is based on knowledge of the direction of
the main stream of flood. The sides of channels are marked by buoys
described as 'starboard hand' or 'port hand', these terms denoting the side
that would be on a mariner's right-hand or left-hand, respectively, when
going with the main flood stream or approaching a harbour from seaward.

Starboard-hand buoys are conical in shape; painted black or in
black-and-white chequers; a top mark (if fitted) of a black cone or a black
diamond; and a light (if one is carried) of one, three or five white
flashes. Port-hand buoys are can-shaped; painted red or in red-and-white
chequers; a
top mark (if fitted) or a red can or red T; and a light (if one is carried)
of two, four or six white flashes. Middle-ground buoys, which mark the ends
of middle grounds,
are spherical in shape. The lights they may exhibit are either white or red
and distinctive,
so that there is no uncertainty as to which side they must be passed.

In cases in which the main channel lies to starboard (when proceeding with
the
main flood stream), or when channels are of equal importance, middle-ground
buoys are painted with red-and-white horizontal bands. In cases in which the
main channel lies to port (when proceeding with the main flood stream) they
are painted with black-and-white horizontal bands. When top marks are
carried, if the main channel lies to starboard (when proceeding in the
direction of the main flood stream) the outer end middle-ground buoy is
marked with a red can and the inner end with a red T. If the main channel
lies to port, the outer end top mark of a middle-ground buoy is a black cone
and the inner end a black diamond. If the channels are of equal importance,
the outer and inner end buoys are marked with a red sphere and a red St.
George's Cross, respectively.
Mid-channel buoys are painted with black-and-white or red-and-white vertical
stripes, Buoys marking isolated dangers are spherical and are painted with
wide black-and-red horizontal bands, separated with a narrow white band.
Landfall buoys, serving to indicate the seaward approach to a harbour
exhibit flashing lights and are painted with black-and-white or
red-and-white vertical stripes.
Buoys marking wrecks in the lateral system are painted green with the word
WRECK in white letters. They exhibit green flashes: one flash to indicate
that the buoy (spherical in shape) may be passed on either hand; two flashes
to indicate that the buoy (can-shaped) is to be passed on the starboard
hand; and three flashes to indicate that the buoy (conical) is to be passed
on the port hand. As well as the lateral system described above, the 1936
proposed buoyage
scheme included a 'cardinal system' designed for use on coasts fringed with
reefs or isolated dangers. The buoys in this system have shape lights,
colours and top marks which indicate whether the buoy is to be passed to the
north, East, South or West. The 1936 scheme allowed the lateral and cardinal
systems to be used in conjunction, but special conical buoys painted with
black-and-white or red-and-white diagonal stripes, mark the places where a
change in the system occurs. There are many systems of buoyage, besides
those described above, in current
use, and the mariner should be perfectly aware of the details of every
system he encounters, from a careful study of the relevant sailing
directions. The essential feature of the 'IALA Maritime Buoyage System A' is
red for
port-hand and green for starboard-hand buoys. The 'lateral' buoys, which
indicate the port and starboard hands of well-defined channels, are painted
red for port-hand buoys and green for starboard-hand buoys. A port-hand is
can-shaped and has a can as a top mark and a starboard-hand buoy is conical
in shape and has a cone as a top mark. By night a port-hand buoy is
distinguished by its red light and a
starboard-hand buoy by its green light. A buoy used to indicate the
direction of deeper water relative to it is
called a 'cardinal buoy'. Such buoys are pillar or spar buoys in
combinations of black and yellow colours, with black double-cone top marks.
A North cardinal buoy is one that should be passed to the north of the buoy,
is painted black above yellow and has a top mark consisting of two black
cones, both pointing upwards. A South cardinal buoy is painted yellow above
black and has a top mark consisting of two black cones both pointing
downwards. An East cardinal buoy is painted black with a single broad yellow
band and has a top mark of two black cones base to base. A West cardinal
buoy is painted yellow with a single broad black band and has a top mark
consisting of two black cones point to point.
A cardinal buoy exhibits a white light, the characteristics of which are
based on a group of very quick or quick flashes, which distinguishes it
first as a cardinal mark and then indicates its quadrant. The distinguishing
flashes are:  North Cardinal: uninterrupted flashes
East Cardinal: 3 Flashes in a group
South Cardinal: 6 flashes in a group
West Cardinal: 9 Flashes in a group.

Cheers
Glenn