Negro oscuro
Hay quienes piensan que decir negro oscuro es incorrecto porque arguyen que el negro ya es oscuro y que por tanto es innecesario agregar ese adjetivo. Sin embargo existen otros adjetivos para designar variaciones del color negro: negro azabache, negro azulado, negro violáceo, entre otros. En francés encontré que se existe noir foncé o sea negro oscuro.
La pregunta es¿sería correcto usar el adjetivo oscuro para clasificar al color negro?
En México circula una burla popular hacia los agentes de tránsito al satirizarlos con frases como "carro negro oscuro, oríllese a la orilla".
10 Answers
jeje, me encanta lo de orrillese...genial.
Hmmm, a mi me suena como blanco claro...en fin.
Lo que sí decimos en España: castaño oscuro
Es un dicho: Esto ya se pasa de castaño oscuro. This is going beyond a joke; this is going too far.
"pitch black" is also used with the same meaning. - samdie 1 hr ago flag
It seems like "pitch black" is always used to describe how dark it is outside or maybe how dirty something is:
"What happened to your shoes, they're pitch black?"
It almost seems to have more of a negative connotation.
"Jet black" seems to be used to describe more positive or neutral things:
"jet black hair"; jet black car, etc.
Has anyone else noticed this? 
I also thought of another expression, although it is probably colloquial:
Black as the ace of spades
I do not pretend to know for sure, but playing devil's advocate, it seems to me that negro oscuro is a redundancy. The Royal Academy defines "negro," as "oscuro,". The other adjectives, azabache, azul etc, are shades of color. So would muy negro, or other superlatives be appropriate.Take a look at the link below and let me know what you think. Just my opinion.
You have to enter the word "negro."
Quite interesting Nicole! I didn't know about jet black.
et2 • noun 1 a hard black semi-precious variety of lignite. 2 (also jet black) a glossy black colour.
— ORIGIN Old French jaiet, from Greek gagates ‘from Gagai’, a town in Asia Minor.
"Negro oscuro" is a redundancy, no doubt, and it is used very seldomly in Spanish. However things like "negro azabache" etc.. make sense because even things that look black at first sight have varying levels of blackness when you put them next to each other, depending on the incident light etc.. That's why certain things, like "carbón" or "azabache", that remain black even under a direct light would be characterized as being blacker than normal black.
When something is really black, I have heard
Esto lo veo negro, negro, negrísimo.
Esto está oscuro como la boca del lobo.
We also say, "It was a dark night."
-Era tanta sangre, en cantidades casi industriales que así, la sangre no era roja, no era de un color negro, un negro oscuro, que me hizo ver cuan oscuro es lo que llevamos por dentro y que llevamos por las venas...
Excerpt from NEGRO OSCURO obra de teatro de Fabian H. Perez.
When ordering hose/stockings, the term "jet black" usually indicates that they are almost opaque because of the color, not because of the thickness of the material as they are actually of a sheer material. Now...I don't know what this has to do with the price of tea anywhere in the world, it's just an observation. 
You are really making me think now Morbo. Yes, dark black/negro oscuro does seem redundant. However, we do use "jet black". I have never stopped to think about why the word "jet" is used.
Here is the definition below, but it still doesn't explain why the word "jet" is used as an adjective to describe the word black.
