オレンジ

How it works

With 好き(すき) (like), the thing you like is marked by が (subject), not the object particle — Japanese treats it as the subject of "is liked". Because 好き(すき) (like) is a な-adjective, the explanatory ending attaches as なんだ (it's that…): a casual んだ (the thing is) that adds a confiding, "the reason is" feel, like sharing a personal fact rather than stating a bare one.