answer: they don’t, but you in your small mind are overgeneralizing.
My mikvah has blue soap. My other mikvah has no soap.
The color is not important, the chemical makeup is.
My kids like blue slurpee, not raspberry. My kids like red slurpee, not cherry slurpee.
You must be a 4 year old, who should not be going to the mikva.
Polish seim issued health regulations for mikvaos in 1920s. Presumably they required soap but not red for commies or brown for nazis. Chofetz Chaim called to both lobby against the laws and also collect funds for mikva upgrades. So if Aguda did the upgrades, they would not use blue and white either. They tried black but old fashioned women didn’t associate it with tahora, so orange was the compromise and we can’t change the tradition since that.