It can do but it's not exclusively "sad". It's closer to "solemn" or "serious". In terms of colour, it can mean deep/dark.

Somber - or sombre in GB English - is used to describe the atmosphere of a place, the mood of an event, or the tone of something such as a piece of music.

Yes, though it is generally a bit of a stronger word than sad. Here's from the Merriam-Webster English dictionary (a very well-known english dictionary): som·ber [adjective \ˈsäm-bər\] : very sad and serious : having a dull or dark color

^^

Such a nice example so as I understand it's the top of depressing(dark color) as Joe mentioned ...