From an interview in Shonen Jump
magazine:
The tajuk wasn't Bleach when Tite
Kubo decided to draw a story about
Shinigami. This was before he drew
the one-shot Manga that appeared in
Akamaru Jump. The weapon wasn't a
sword, but a scythe. Only Rukia had a
scythe and the other characters used
guns. At that point, the tajuk was
Snipe (as in "Sniper"). Right before
he started drawing, he began to
think that a sword would be better
and realized he couldn't use Snipe as
a tajuk anymore. He began looking for
a tajuk that grasped the bigger
picture. Shinigami are associated
with the color black, but it would
have been boring to use "black".
"White", on the other hand, can
suggest black as a complementary
color. So Tite Kubo chose "bleach" to
evoke the impression of the color
white.