"Dewi Lingo's car is purple."
Translation:Mae car Dewi Lingo yn borffor.
Good question. I had just answered a question in which purple was borffor now suddenly it's biws? Who moved the goalposts?
No goalposts have been moved - the word "piws" is another word for "purple" in Cymraeg :)
car Dewi Lingo is already definite -- like "Dewi Lingo's car" in English.
We don't say "the Dewi Lingo's car" or "Dewi Lingo's the car" in English, nor "y car Dewi Lingo" in Welsh.
(Not like, say, the Italians who would say "the his car".)
Maybe according to the dictionary but in practice "piws" is often just used to mean "purple".