Sometimes it is difficult to remove the color of the menstrual blood from a garment. In spite of using different detergents, traces of a pale color remain but there is no apparent change in the color of the water dripping from it. Is the garment pure in this case and fit to pray with? May Allaah reward you.

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah  and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The presence of the color of menstrual blood on the garment after washing it is harmless. The Prophet said to Khawlah, may Allaah  be pleased with her: "Water is sufficient (for washing) and the remaining color does not harm you." [Al-Bukhari]

Allaah  Knows best.