물들다 : i dunno the correct English term for this but i think it means - shower/pour/ cover/ wash
So based on the lyrics before;
내가 만일 하늘이 라면
If i am a sky by any chance
그대 얼굴에 물들고 싶어
I want to shower/cover/wash your face with it (the sky)
Please correct me if im wrong