I take a beginners spanish course in school and came across this blip one day. I was trying to describe a girl in a photo wearing pink socks as la niña lleva calcetines rosas. My teacher then said that I would have to change the rosas to rosa because it didn´t sound natural, then came to the realization that all color adjectives naturally ending in -a stay singular regardless of the noun they are attached to.
We didn't get the time to corroborate the theory with non-color adjective as it was the end of class, but does it apply to all feminine, i.e. -a ending adjectives? Or is the theory correct for all such color adjectives in the first place?
Edit: I believe the question I had unknowingly duplicated had the same essence as mine did, but the answers on the use of the noun/adjective café did not answer my question from the perspective of feminine adjectives, at least from what I understood of it.