Thoros Beta is one of the most colourful worlds the Doctor has ever visited with fluorescent green skies and pink seas.
The sixth Doctor and Peri visited Thoros Beta when the Doctor was investigating laser weapons sold to Thordon and Krontep. Whilst there they found Sil, and the other Mentors, trying to save the life of their leader Kiv.
Evidence of the visit was distorted and used as evidence in the Doctor's trial, and the Doctor was taken away by the Time Lords before events were finished.
- Thoros Alpha