Can you help me in this matter?
بسم الله الرحمن الرحيم
It is enough to wash the impurity, it is not necessary to remove its colour or mark. If you washed away the impurity, the shalwar and qamis shall turn pure though the mark or colour remains. It is not necessary to remove the mark in order to get purity. You may offer salah with the mark too.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.