1) I have done ghus and I have been seeing after my menstruation a white substance, is that haydh or it is tahir substance?

2) How about the yellowish discharge it is paak too?

by

1) White discharge is paak

2) If the discharge is similar to what you see during your non haydh days then it is paak. If it is white and looks yellow on tissue or pad due to the contrasting colours then it is paak.

However if it has spots of blood or can be said to be remaining blood coming out then it will count as haydh and you will have to redo your ghusl.

If you have doubt of there being blood, then regard it as continuation of haydh and do ghusl