"It is her dark green dress."
Translation:Det er hendes mørkegrønne kjole.
I asked my Danish friend: its because if the subject is "it" you always use det
I also had this question. The best answer I've found so far is here:
When the noun is definite (e.g. her dress/the dress/that dress...) the adjective has the plural/definite form, which often has a -e ending.
En mørkegrøn kjole
Hendes mørkegrønne kjole
Thanks so much! That explains it perfectly. I've been wondering about this for months.
"Det er sin mørkegrønne kjole" should be accepted as well, since it would then mean "her own". Or am I missing something?