The red color in the flag of Nationalist China represents the land of China itself, or the Han Chinese as opposed to the other races of China.
The White sun on the blue colored background was the flag of the so-called "Kuo Min Tang," or the nationalist party formed some one hundred and twenty years ago, in 1891 by "Sun Yat-sen."
Chiang Kai-shek who took over from Sun Yat-sen, formed a government in 1928 which adopted the KMT flag in a red colored flag-field. From the thirties and onwards this government was at war with both the Communists and the Japanese, but in 1949 was driven to the island of Taiwan, where it still is in existence.
The flags are hoisted on Taiwanese flag poles throughout the island.