I've only known or seen "There be Dragons" as interchangeable with "Here be Dragons" as in the context of internet meme maps that make fun of countryside areas. Like this one. However, In a different post on ELL I found an answer with "There be Dragons" in a context I couldn't quite figure out. From the proficiency of the written answer I am assuming this usage of "There be Dragons" has a distinct meaning that isn't an anomaly specific to that particular English user.
"These terms have comparative (darker, fairer) and superlative (darkest, fairest) forms and can be used of people of any complexion. So you could describe a white person with brown hair as being darker than a redhead.
So you could, if you had reason to, describe someone as simply a very dark African-American (though "African-American" is really not very common outside of America). Although it is worth noting that there be dragons. However, it is not necessarily politically incorrect or offensive at all and such terms can obviously be very useful if discussing racial politics or prejudice or whatever."