Bethselamin

Bethselamin was a planet that lacked the colour purple and had an unbroken history of peace.

When the Fourth Doctor, Romana II and K9 Mark III arrived on the planet to search for the Silver Bail of Peace, the Doctor immediately complained about the lack of purple.

Romana II was once absent during a visit the Fourth Doctor made to Professor Chronotis, as she was standing for election as President of Bethselamin. (PROSE: Doctor Who and the Krikkitmen)

Behind the scenes
Bethselamin was a planet mentioned in The Hitchhiker's Guide to the Galaxy, which had an overflow of tourists.