Does the bleach here refers to a blue dye, but less blue one, as some of the blue has been removed?
The rain seeped into the gap between the health sandals and her feet, just like it was seeping into everything else. Kerala was steeped in water, as if someone had pushed it in and pulled it out, like her mother used to steep white clothes in indigo bleach in a plastic bucket in their backyard. People were prepared, as they should be, in a state where it rained six months a year.
Indigo bleach is a particular dye used for making bluejeans, or denim.
The passage you're quoting from uses the word "blue" frequently, probably for symbolic or literary reasons.
The parking lot she'd just walked through where covered in blue and silver rain covers, umbrella covers stuck out...
The colour of her salwarkurta was the same as the board, a deep midnight blue.
The author may have intended to use blue because of its common metaphorical implication of loneliness or isolation.
Indigo is a challenging dye because it is not soluble in water. To be dissolved, it must undergo a chemical change (reduction). Reduction converts indigo into "white indigo" (leuco-indigo). When a submerged fabric is removed from the dyebath, the white indigo quickly combines with oxygen in the air and reverts to the insoluble, intensely colored indigo. When it first became widely available in Europe in the 16th century, European dyers and printers struggled with indigo because of this distinctive property.
from Wikipedia "Indigo Dye" - https://en.wikipedia.org/wiki/Indigo_dye
