Pluralisation of Colours
Do all Spanish colours have a plural?
2 Answers
the answer to your question is yes.
----> zapatos negros
----> ojos azules
-----> manzanas rojas
-----> camisas amarillas
-----> medias blancas / calcetines blancos
-----> etc etc etc
Although you have an answer from a native speaker, I will provide a little bit of information solely for consideration taken directly from a reputable learning site that indicates that although you can pluralize colors, in some cases some of them are treated by some speakers as invariable adjectives and not pluralize ones that are derived by some nouns:
I am only copying some information, please consider reading the entirety of both sites.
http://spanish.about.com/od/adjectives/a/colors.htm
Note for intermediate students: When using colors derived from nouns, it isn't unusual for speakers to omit the word color (or color de or de color), so that a mustard-colored house would be una casa mostaza. When a noun is used in such a way, it is often still treated as a noun rather than an adjective, so it doesn't change form as adjectives typically do. (Some grammarians consider nouns used in this way to be invariable adjectives, that is, adjectives that don't change for number or gender). Thus "mustard-colored houses" would be casas mostaza rather than casas mostazas (although the latter is also used).
The more often a noun is used as a color, the more likely it is to be treated as a regular adjective, that is, one that changes in number with the noun being described. Often, different speakers won't always agree. Thus, the coffee-colored shirts may be described as camisas café or camisas cafés, again depending on the speaker. More information on this phenomenon is available in a separate lesson on invariable adjectives.
http://spanish.about.com/od/adjectives/a/invar_adjective.htm
Answer: The short answer is that there is a variety of ways of saying "orange cars," and that both coches naranjas and coches naranja are among them
.Note- it would always be coches anaranjados (since anaranjado is a true adjective, not a noun mimicking an adjective), but in the above, even when pluralized, they are not gender matching.
Just an attempt to make things more confusing. But maybe that is why you asked the question.