The mangaka behind the popular shounen anime and manga Bleach, Tite Kubo, answered this is an interview. Kubo sensei shared that the reason the title is Bleach is because of how the color black can be ‘bleached’ to white, which is its complementary color.
He stated that at first, the weapons used, originally the characters used guns and only one character actually used a scythe, in the manga allowed him to use the title Snipe, which was its actual original title. However, Shinigami, the main job description portrayed in the shounen manga, use scythes.
Shinigami, according to the Japanese culture are associated with the color black. They are essentially Reapers, according to Japanese folklore. Something akin to grim reapers but dressed in impressive yukatas.
Hence why he chose Bleach. White is a complementary color to black and once black is essentially ‘bleached’ it turns to white. This is why the title to the hit anime is Bleach due to the mangaka striving for a much thought-provoking title.