By the time I started learning Spanish, I'd already studied three languages formally. Two of them, Latin and ancient Greek, have extremely complicated grammar. So I was well-versed in all terms grammatical---all the parts of speech, noun and adjective declensions, verb tenses and aspects and voices and persons. I consider myself somewhat of an expert on the structure of the languages I know.
I was shocked, therefore, when a fellow student in Mexico brought up something I'd never even considered before: order of adjectives. You can't say "a black small cat"; it has to be "a small black cat". I don't remember learning this in my English grammar classes, but as a native English speaker I can tell you what sounds right and what doesn't.
There is, in fact, an accepted order of adjectives in English, depending on the quality described. Size comes before color. Other languages have their own orders (see here for a description in Spanish), which seem more or less similar, with accommodations for non-English constructions like postpositive adjectives.
What I find curious is the fact that I never learned order of adjectives explicitly, not in English or any of my foreign language classes. Is it because it's more of a custom than a rule (though making the distinction is always a little dicey)? Or because there's some inherent hierarchy based on how humans perceive material qualities (I find this a little hard to believe)? I do see the subject mentioned occasionally in ESL classes. I'd love to know from my readers who learned English formally in other countries whether this topic was ever discussed.