Found this when searching, easy link for future reference: https://www.duolingo.com/comment/26961672/fonc%C3%A9-vs-sombre
So as I understood it:
Foncé appears to be used when talking specifically about colours, and is used more relatively in a context of "that is a dark(er) shade of the colour"
Sombre can be used for anything including colours, except when it's a specific colour. It can also mean dark in the sense of 'grim', 'gloomy', 'grave', 'sombre', 'dark', 'sad', 'murky' or 'not enough light'. e.g.; "black is a dark colour"
Ok so vous avez un costume sombre, is fine because sombre is referring to the suit.
Nous avons des chaussures sombres is fine for the same reason.
I guess that means that la bière est sombre should also be accepted as in this instance sombre doesn't refer to a colour, but a thing.
It's also worth noticing that in the context of these sentences sombre isn't being used figuratively although perhaps given a different context these sentences could have a figurative slant.
Thank you; this was very helpful. However, in the iOS version, not all of these choices appear when I click on REPORT:
"The audio does not sound correct. The dictionary hints on hover are wrong or missing. The French/English sentence is unnatural or has an error. The "Correct solution" is unnatural or has an error. My answer should be accepted"
Please: When do we use foncé and when sombre? I have read the explanations that foncé is used with colors. Beer is not a color, but was the correct choice, supposedly because of the reference to the color of the beer (?? dark vs. light beer). Now here foncé is not used, even though we are still referencing color (dark colored shoes vs. light colored shoes). Je ne comprends pas du tout.
This was discussed briefly in 'adjectives': https://www.duolingo.com/skill/fr/Adjectives-1/tips-and-notes "some adjectives have the same masculine and feminine form, especially those ending in a silent -e (e.g. riche)"
So 'sombre' is used for the singular form for both masculine and feminine nouns. 'Sombres' is used for the plural form of both masculine and feminine nouns.
Found this site that describes how to conjugate adjectives to a feminine form, in case you need it: http://mylanguages.org/french_adjectives.php