"The blue ceiling."
Translation:Η μπλε οροφή.
Please always quote your entire answer when you have a question.
For example, did you write Η μπλέ ταβάνι, perhaps, when ταβάνι (like pretty much all nouns in -ι) is neuter? η is the feminine definite article and works with feminine nouns such as οροφή but not with neuter nouns such as ταβάνι.