As a Brazilian, not much. Throughout my entire lifetime, I saw some Brazilians there and there wearing Halloween costumes but it's not as popular here as "quermesses" (kirmess, church fairs, happening mostly on Brazilian's interiorian towns), Carnival, Christmas or some "important" soccer game (such as Corinthians vs Palmeiras, or Flamengo vs Fluminense).
To me, particularly, no holiday (nor soccer games) holds any importance or meaning. In the end of the day, it'll be just capitalism mesmerizing people to spend money on temporary things.
Darker doesn't always mean blacker. Symbolically, a blood moon is "darker" (as in "ominous" and "eerie") than a new moon. The red color has many meanings, ranging from passion to wrath. Even after science emerged to explain such phenomena (the red color being just the longest wavelength part of visible electromagnetic spectra, the blood moon being just a combination of physical and astrophysical factors such as Rayleigh scattering and planetary alignment, etc), the blood moon still gets a "bad omen" vibe nowadays, a vibe that's absolutely not present during new moons (it's worth mentioning that they happen once or twice every month, differently from a blood moon which is a somewhat-rare event).