No one has offered an official explanation, but it's more likely the color comes from sewage, pollution or a water treatment process.

没有人提供官方解释 但这颜色更可能来自地下污水 污染水或是水处理。

youdao

As of now, no such treatment has been used successfully to lessen or remove color, that is why you can always be sure that they are not treated.

截至目前，没有这种治疗已被成功地用来减轻或消除的颜色，这就是为什么你总是可以确保他们未得到治疗。

youdao

Trichroism . As of now, no such treatment has been used successfully to lessen or remove color, that is why you can always be sure that they are not treated.

截至目前，没有这种治疗已被成功地用来减轻或消除的颜色，这就是为什么你总是可以确保他们未得到治疗。

youdao

The amendment to the state constitution would prohibit the state from granting preferential treatment or discriminating against any individual or group on the basis of race, sex, skin color, ethnicity or national origin.

CNN: Variety of proposals on ballots in 37 states