"une personne" is an individual, no specific gender. It may refer to a man or a woman. therefore, "c'est une personne froide" may translate in "he/she is a cold person".
Because "une personne" is necessarily a human being, you cannot use pronoun "it".
The word is feminine, but it can refer to both genders.
Une personne = A person
Actually, it should be "It's a cold person." The reason is because if you were identifying a woman as a cold person, you would use "elle." The reason why it's "une personne" is because "personne" is always feminine.
If Duo had constructed the example the way you suggest then students might not notice that in this sentence it is the object that is feminine not the subject.
The gender of the subject is not specified which in French means it has to be taken as masculine. Masculine is assumed unless indicated otherwise.
This particular sentence introduces three of four concepts at once that beginning students find tricky.
"c'est une personne froide" can translate in: - he is a cold person (re. rule of he/she + is + noun -> c'est un/une) - she is a cold person (same as above) - it is a cold person - this/that is a cold person.
In this sentence, "une personne froide" is not an object, but an attribute (after verb être, paraître, sembler, devenir, demeurer, rester, all being "state" verbs, the noun qualifies the subject, so it is not an object but an attribute).
"c'est" is used with he, she and it + verb BE + modified noun (= article + noun, most often)
On a different note. SiteSurf said below the meaning here is figurative " he/she is a cold (hearted) person" Would it be "C'est une froide personne " if it was literal, meaning "he/she is a cold (literally to the touch) personne"?
In absolute, the place of the adjective should not change, even if you were in the morgue.
My french teacher always said not to say "il est froid" or "elle est chaud" because it would imply that they are sexually hot or cold. Same with "il est bon." Is this true?
le radiateur est froid = il est froid
l'eau est chaude = elle est chaude.
Only very exceptionally, when you are surrounded by people you should not ever talk to, what your teacher mentions may have sexual connotations. Otherwise, feel free to use those.
Same in English.
If your English is clumsy because you are learning the language and people see you as making mistakes, then she is hot will generate a snicker from some people. Even when it is clear that the person is hot because they are sweating and complaining etc. some people will laugh.
Someone teaching English as a second language might caution students to be careful using such phrases especially around students. Sensitive students hearing this warning might draw the conclusion....never say she is hot .........or similar, because the embarrassment would be extreme.
Of course, a native English speaker would have no hesitation describing someone as hot or cold or good, if that is what they were.
I assumed this could mean "he/she is a cold person" in an emotional sense, so I translated it as "he is a frigid person."
This was marked wrong, but is it acceptable?
No, the adjective you are to learn here is "froid, froide, froids, froides". Also, "frigid" has sexual connotations that "une personne froide" does not have.
can i not use "they are a cold person" in this context, since i do not know if THEY are a man or a woman.
With unusual words like personne and bébé, if you only have that phrase you have no gender information. This is a vast difference between French and English. Does any modern (s)lang help?
If you don't want to use "un bébé", you can say "un nouveau-né" but you still don't know if the baby is a girl or boy. If you don't want to use "une personne", you can use "un individu", but you still don't know his/her gender. Same story with "un témoin" (a witness), "une victime" (victim) and a few others.
This is not a vast difference, since in English you don't know anyway.