Red and blue - colors of the circle in the middle of the Korean flag. Guessing this was intentional
Indeed. Since before it was just red (the red sun disc of Japanese flag) , the boy was sad - which can symbolize the burden or emotional weight mugyeong feels while representing that country.
but we also know that yukio had realized it way earlier that only if mugyeong was running with the taegukgi on his back , he'd have been much faster and most probably win for his home country .
The final line can suggest that mugyeong will then be finally liberated from his previous burdens to find a future/path of his own.
"BOY RUNS, HIS BACK CAST IN A SAD, RED LIGHT...
...PERHAPS SOMEDAY, I PRAY, AN ADJOINING BLUE MAY ALSO SHINE BRIGHT
THEN, MY BOY SHALL BE ECSTATIC AND RUN WITH DELIGHT...
...DISAPPEARING || INTO THE DISTANCE WITH NO SOUL AHEAD IN SIGHT"
I wanna bow my head to the author as well as the translators cause wtf these lines were so beautiful.
gonna start a manifestation circle so that yukio and mugyeong get reincarnated and meet each other in another lifetime