Auriculares rosa
 

Hi,

Duo again :D

I bought you those pink headphones that you like so much.

My translation, accepted:

Te compré esos auriculares rosas que te gustan tanto.

Another correct solution (by Duo):

Te compré esos auriculares rosa que te gustan tanto.


I used to think that the agreement in number is mandatory. What is it?

Some Spanish adjectives have 4 distinct forms that differ by gender and number (rojo/roja/rojos/rojas), some have 2 distinct forms that differ only by number (azul/azules), and some adjectives are invariable (rosa, macho, hembra, and others).

Rosa happens to be one of many color words that historically have been invariable when used as adjectives. However, it seems that some native speakers now consider rosa to have both a singular and a plural form.

You cannot tell whether a particular adjective is invariable or not just by looking at it: you have to learn it individually for each adjective. However, there are some guidelines that can help you make a reasonable guess regarding whether a particular adjective varies by both gender and number, varies only by number, or is invariable. In any case, a noun that is being used as if it were an adjective typically is invariable when used that way.