Since 'hvor' is 'where', would 'hvorfor' be similar to 'wherefore', which was early modern English for 'why' (such as in Romeo and Juliet: "wherefore art thou Romeo")
That sounds like something someone would tell me when I'm baking something...
As long as they're not asking hvorfor er det sort? I think you'll be okay (;
they are probably questioning the black and brown stawberrys bears and blue animals were eating in colours
It's because "det" is used, which is neuter. The adjective follows its gender, hence it's brunt, and not brun.
If you say "Why are they brown?" it would be "Hvorfor er de brune?"