that's totally common for asians, I don't know about other races. I was pale when I was younger but as I grew up my skin got darker. The opposite happened to my cousin
me too! i was tan when i was younger but i got paler as i got older
It's also most likely based on life style. Doosan as a energetic kid probably spent a lot of time playing outside with the other boys so he got a tan. But as an older kid, he probably spent a lot of time indoors playing arcade games + part time job, so he got lighter with the lack of sun exposure.
Same with Taesan, he was a pretty shy rich kid so he stayed indoors a lot. He probably stayed outdoors a lot as he got older.. (there's hints of him wanting to be an athlete, so he probably had practiced outdoors) and also probably cause his last memories was of a tanned Doosan. kid!Doosan was his idol, so he might have also subconsciously tried emulating that?
Soooocuteeee (≧∀≦)
But why did they switch skin color while growing up lmao