I randomly went to wiki TELETUBBIES, and this funny article came up.
About saying goodbye:
All the Teletubbies say "Bye-Bye" three times. The narrator bids each Teletubby goodbye, and they disappear, but reappear a moment later saying "Boo!". The narrator then says "No", (which they copy) and proceeds to say goodbye to each Teletubby again. The sun is then shown setting, and the Teletubbies each say goodbye again, before jumping down a hole in the roof of their house. Finally, one Teletubby says goodbye a fourth time - they pop out of a hole in the house and say "Bye-bye!".
About the food:
Their diet seems to be almost exclusively "Tubby Custard" mispronounced as Tubby Tustard by the characters (which is created by a Tubby Custard machine and consumed by sucking through a spiral straw) and "Tubby Toast" (circular toast with a smiley face on it), and they are spectacularly messy eaters.
In one episode, the "Tubby Toaster", the machine that makes "Tubby Toast" went seriously wrong and filled the Teletubbies' house with toast. Fortunately, one of their companions is Noo-Noo, a vacuum cleaner.
About Dipsy:
His face is also notably darker than the rest of the Teletubbies, and the creators have stated that he is Black.
About Po:
She has been stated by the show's creators to be Cantonese, and as such, she is bilingual, speaking both English and Cantonese. Po is voiced by Pui Fan Lee.