"Culoarea macului este roșu."

Here "The poppy's colour is red" should also be accepted (see English grammar)

culoarea macului este ....... Rosu sau rosie? cum se face acordul aici? va multumesc anticipat de clarificare

In a multiple choice question macilor should be accepted as correct in addition to macului, surely. It's impossible to know that the sentence required is the translation of "the colour of the poppy is red" amd not "the colour of the poppies is red"