What is the meaning of "Then I would see on it a spot or spots" in the Hadith of Aisha, may Allah be pleased with her: "She used to wash semen from the garment of the Prophet, peace and blessings of Allah be upon him, then I would see on it a spot or spots"?

Al-Bukhari narrated in his Sahih that Aisha, may Allah be pleased with her, used to wash semen off the garment of the Messenger of Allah, peace and blessings be upon him, and he would then go out for prayer with the traces of the washing still on his garment, meaning water stains. It is possible that this refers to the wetness of the water with which the garment was washed, or the traces of ritual impurity that were washed away. Al-Bukhari used this hadith as evidence that the persistence of traces after the removal of the substance, in the purification from impurity, does not cause harm.