"The shoes are dark brown."
Translation:Les chaussures sont marron foncé.
Found this explanation on reddit: Both can mean "dark", you're right. I give you here the most common uses, this is not exhaustive.
"Foncé" is only used for colours, while "sombre" works in any context (including colours, so "une couleur foncée" or "une couleur sombre" mean almost the same. However, if you speak of a specific colour, you must use "foncé", so "du bleu foncé").
"Sombre" can also be used for :
"not enough light", for example "Lorsque le soleil se couche, il commence à faire sombre."
in the figurative sense, it means something like "sad and grave". "Le 11 septembre est un jour sombre dans l'Histoire des États-Unis."
I cannot find a sentence that describes a shirt as dark grey using "sombre" in the database. If you encounter it again, could you link the sentence discussion here? It's incorrect and should be fixed.
I do know of several sentences where the clothes or shoes are described as "sombre" or simply dark.
Nous aimons les vêtements sombres. We like dark clothes.
Nous avons des chaussures sombres. We have dark shoes.
I'm afraid that's not quite it. Foncé has nothing to do with how depressingly dark a color is. It just means "dark."
rouge foncé → dark red
bleu foncé → dark blue
orange foncé → dark orange
Sombre can be used with the word "couleur," une couleur sombre or a dark color. It can also be used figuratively as mrgabri_l stated, un jour sombre, or a dark/sad/grave day.
As far as I understood, foncè is for color property, as one color is brighter/darker than another. While sombre relates to color intuition. So sure sombre and foncè can both be used to describe dark in English, one is what Duolingo wants you to use based on dictated french sentence. This also happens with plurals and female/male driven sentences. Funny enough, in my country's language (hebrew, no french for Hebrew speakers yet) there is a word that resemble foncè and another for sombre.
This is actually one of those weird French grammar rules - for compound colors adjectives (i.e. colors that are 2 or more words), the words are invariable and just always take the masculine singular form, regardless of the noun. This applies not just to invariable colors like marron, but also colors that normally agree with their nouns like bleu or vert. A couple of examples:
"Light blue eyes" would be "des yeux bleu clair", not "des yeux bleus clairs"
"A black-and-white photo" would be "une photo noir et blanc", not "une photo noire et blanche"
I can tell you that I was taught that "brun" is primarily for hair, eyes and fur, whereas "marron" describes just about everything else.
Our resident French grammarian, Sitesurf, has stated in another sentence discussion:
"Brun(e)(s)" is mostly used for hair and skin, not to describe other brown things.
Therefore, in France's French, "brown shoes" are "des chaussures marron".
I have heard that in Canada that brun can describe objects too, and have seen examples of it online, but for now the French taught is from France.
Colors can be both nouns and adjectives. As nouns, colors are usually masculine.
Le rose. — The pink.
As adjectives, they agree with the nouns they modify except in two cases.
First, colors derived from nouns (e.g. fruits, flowers, or gems) tend to be invariable with gender and number. Orange ("orange") and marron ("brown") are the most common examples.
La jupe orange — The orange skirt
Les jupes orange — The orange skirts
Les chiens marron. — The brown dogs.
Second, in compound adjectives (les adjectifs composés) made up of two adjectives, both adjectives remain in their masculine singular forms.
Sa couleur est vert pomme. — Its color is apple-green.
J'aime les robes rose clair. — I like light-pink dresses.
When colors are modified in French they become invariable; this means they don't change depending on the noun. Whenever you have a compound color (two parts) in French, it stays singular/masculine.
Thus it is always:
dark brown → marron foncé
light red → rouge clair
pale blue → bleu pâle
No, when a color is modified by another word, it becomes invariable. It does not form agreements with the noun.
A compound color always looks singular and masculine .
a dark brown shoe → une chaussure marron foncé
pale yellow birds → des oiseaux jaune pâle
a light blue chair → une chaise bleu clair
If you are using the web version of Duolingo, you should have access to the entire sentence discussion. You may find that your question has already been asked and answered within the discussion.
It's a good idea to check it out before posting. ;-) https://forum.duolingo.com/comment/26751313$comment_id=28247552
Foncé means "dark" but it not a color.
The point of this exercise is to demonstrate that compound colors (gris clair, jaune pâle, vert foncé, etc), are invariable. First comes the color and then the modifier, and they do not form accords with the noun described, but are always singular/masculine.