Comet C/2025 Lemmon is a dynamically new comet making its first recorded passage through the inner solar system, arriving fresh from the Oort Cloud. Its green colouring — visible in longer exposures — is caused by diatomic carbon (C2) molecules in the coma fluorescing under ultraviolet sunlight. First-time visitors from the Oort Cloud often produce dramatic displays as pristine, volatile-rich ices encounter solar radiation for the first time.