If you have the audio exercise, only the feminine form (blonde) will be accepted. You will know by hearing the final "d" pronounced. For the masculine version "blond", the final "d" is silent. In translating from the English, either "blonde" or "blond" will be accepted. Unlike other language learning sites, the voice of the speaker is not a gender clue. Duolingo uses either male or female voices to read any sentence so you could have a male voice say "je suis une fille" or a female voice say "je suis un homme". That's just the way it is.
Wait...really? I've never heard the male voice. I thought maybe it let me listen to the female voice because I'm a woman and it wanted me to hear/practice the gendered nuances (not sure if there's a term for that - I'm thinking, for instance, how French women seem to speak from the top of their mouth while men seem to talk from a wide throat...if that makes sense to anyone but me...).
Duolingo doesn't know your gender or your age or anything about you other than you are signed up here to study French. If you have the "type what you hear" exercise, the word is pronounced "blonde" with the final "d" being clearly enunciated. The masculine form is "blond" in which the final "d" is silent.
The gender of the speaker does not change the pronunciation. Imagine he is quoting what a woman said. He has to use her words exactly, not change them to match his gender. This is a good exercise to get you listening to the actual words and not to make assumptions based on the speaker. Il a dit « Les hommes disent "Nous sommes blonds" et les femmes disent "Nous sommes blondes". » Oh no! Now a single male person is using the plural forms! How confusing! ;-)
FYI- Also: brunette, brunet. Though the latter isn't used much nowadays, which is why you don't much hear men being referred to as brunets. We do also have a couple of gendered nouns; though they're usually referred to as 'it'. For example, it's not uncommon for a ship or country to be referred to as 'she'. Here endeth today's lesson :)
If you got this as an audio exercise it can only be feminine (not female) because the "d" is pronounced. If it is « Je suis blond » (silent "d") then the speaker is talking in the masculine form. Note that it could be a woman repeating what a man said:
- Il a dit « Je suis blond »
or a man repeating what a woman said:
- Elle a dit « Je suis blonde »
Actually, English does have blond/blonde as a gender based spelling type noun. The distinction is drawn much less commonly than when accuracy in English was considered very important but the difference does still exist.
It is true that the tendency to default to masculine in English was always present when using blond as an adjective but it is not wrong to use the feminine form even as an adjective.