Korea's  Sam-Taegeuk  Symbol
the Korean-style Sam-Taegeuk
[three-part Grand Ultimate] Symbol,
used in Korean Shamanism, Neo-Confucianism, Daoism and Buddhism
Symbolizing the Cheon-Ji-In Trinity:

Blue = Heaven    Red = Earth    Yellow = Humanity
Heaven influences Earth, which influences Humanity, which influences Heaven...

or, in other interpretations, Blue = Heaven, Yellow = Earth and Red = Humanity
(depending whether Red is seen as the color of Chinese farming-soil or of human blood, and Yellow is seen as the color
of soil or of human skin; the Chinese Emperor wore yellow robes in representing Humanity as the "Son of Heaven".)

It doesn't seem to matter which color is placed where.
The Korean Sam-Taegeuk symbol above is
related to but quite different from the better-known
Chinese Yin-Yang 陰陽 yīnyáng 阴阳 symbol (right),
also called the Taijitu 太極圖 Taìjí tú 太极图 or T'ai-chi,
literally "Diagram of the Supreme Ultimate", most
frequently used in Chinese Taoist and Neo-
Confucian philosophy and cultural arts.
Stained-glass-mosaic window in the Hyehwa
Catholic Church of Seoul -- Heavenly Blue is on top.
On the tiled walls of the Dongnip-mun Metro Station
in NE Seoul below Inwang-san,  Red is on top.
A very interesting variation was found on the flag of a major Shamanic Association,
photographed at their Sanshin-je Ceremony at Inwang-san in April 2009.  This could
be called an "O-Taegeuk", with five colors (Yellow forming the center, which is
traditional in Five-Directions Theory), apparently derived from the classical Five
Phases (Elements) Theory of Chinese Daoism, called Ohaeng in Korean.  The Five
Phases known as Metal, Wood, Water, Fire and Earth are usually represented in Five
Colors: White, Black, Blue, Red and Yellow -- but here black has been replaced by
green.  An official of this group told me that this was an "ancient original Korean
Ohaeng, different from the Chinese system.  I know nothing further about this claim.
the Neo-Confucian two-part Taegeuk is used at the center of the
Republic of Korea's Taegeuk-gi National Flag -- see the history here
Symbol and name "Sam-taegeuk" used by a nationalistic organization at a festival
Neo-Confucian two-part Taegeuk, llight-red & blue on royal-red background, with extra-long
swirls, on the gate of the Shrine to "Hoeheon" An Hyang at the Sosu-seowon Academy
6-part  Taegeuks  on the Great East Gate of Seoul  (Dongdae-mun, or Heunginji-mun)
two-part elongated Taegeuk and Palgwae, together seeming to represent the universal Sun {Hwa-eom Enlightenment?},
with 3 large flowers and 4 small ones, in a good-fortune Joseon folk-painting, in the Yeongwol Minhwa-do Museum
on the Dharma-Drum of Naejang-sa Temple -- the blue has faded to black
A typical and common Korean
Sam-taegeuk Fan, used in
Shamanic and other rituals,
or just personal fanning....
Often sold as a souvenir.
Those colors in triplet, on a security door of an ordinary shop in Seoul -- coincidence or deliberate??
Another very important, deeply meaningful Triplet -- the "Three Spiritual Treasures"
三神器, Samshin-gi in Korean [that 器 is an archaic character       , うつわ in historical
kana, meaning "container, vessel; a tool, a utensil; one's degree of ability: talent, calibre;
female genitalia: a vagina, therefore an origin of life; gi 기 in hangeul],  of an Emperor --
bronze mirror, bronze sword and a cashew-shaped green jade.  This set of 3 precious
items symbolizing sovereignty originated in ancient-most China, but was later abandoned
in usage and a specific set has not been found (although many such ancient artifacts as these
three have been recovered in central China and southern Korea, and are in museums) -- if the oldest
imperial tombs are ever excavated, such sets might be found.  This particular set was
found in the Nara City tomb or tomb-temple of the first Japanese king of Honshu Island
to {illegitimately} claim the title "emperor", around 600 CE.... it is not clear whether these
items were meant to be buried forever with him, or to be handed-down to successors.  
No such set seems to have been used by Korean kings of the Three Kingdoms and
Three Dynasties, as they did not pretend to "emperor" status except in two brief instances.

Anyway, they can be symbolically associated with the Sam-taegeuk symbol and Heaven-
Earth-Humanity concept in that the mirror represents Heaven (round shape), the jade is
Earth (best kind of terrestrial stone) and the sword represents Humanity (standing long
and straight-up, and a tool used by people to establish rule over realms).