Blue! Wait! No, I mean-- launches off bridge
Anything wrong with "which is your favourite colour?"
Nothing per se. But it strikes me as more likely to be suggesting that the listener is being asked to choose among colors laid out before them, instead of being asked in the abstract.
什么 instead of 哪个 implies it could mean what are their favorite colors (plural), correct?
It's indefinite as to number, and the answer could be one color or more than one.
If you wanted to specifically ask for more than one color, you could use " 哪些".
wouldn't this be better?
"What colour do you prefer?" not accepted on Feb 19th 2018. Reported.
"What color do you like the most" is accepted. March 16, 2018
It was not accepted today
Favourite is an absolute (non-gradable) adjective, so something cannot be more or most favourite.
FWIW the Chinese doesn't say "favorite," but "most liked," which I convert to favorite.
Correct answer was accepted. Europe, December 3, 2018. 7:40 am
"What color do you like the most?" is correct, but was not accepted.
Where did the 顔 come from? Doesn't 顔色 mean "dye" or pigment"?
The Chinese can mean "pigment", but it's also the normal way to say "color". You've used the Japanese variant, which, in Japanese, apparently means "complexion". Both, it seems, can also refer to facial expression.
"What colour do you like best" is most direct, and correct translation but not accepted july 2020.