On the last day of my menses, I saw a colored discharge before making ghusl (bath taken in case of major ritual impurity) and took a bath assuming it to be the last, colored (reddish) discharge. I made the intention that if my period was over, then that would be a ghusl, and if not, then it would be a normal bath, and I did ghusl. However, I did not pray because there was a 50-50 possibility that my period had not ended or that I might continue getting a colored discharge. I resumed praying after seeing a white discharge but did not renew my ghusl. Was my ghusl valid, and if not, then do I have to repeat all those prayers? I usually perform ghusl after seeing the white discharge, but sometimes I am in a hurry (or lazy, or I know that later in that day I might be in a situation where I may not be able to take ghusl at the exact time, like if I am outside) and when I see a little red discharge then, I assume that it may end (later in that day) and make the intention for ghusl as if it had ended and perform ghusl because preventing is better than curing.

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 is His slave and Messenger.

The end of the menstrual period is not known by those colored discharges; rather, such discharges are part of the period and seeing them is not a proof that the period is over. The end of the period is known by one of the following two signs: either by dryness, which is by inserting a piece of cotton in the vagina and it coming out clean without any trace of blood or yellowish or brownish traces, or by the white discharge, which is a white water by which women know that the bleeding has stopped. For more benefit, please refer to fataawa 90315and 174955.

Therefore, if you see one of these two signs, then you can judge that the period is over and you should then perform ghusl.

Since the matter is as you mentioned, then you have performed ghusl before your period was over, so your ghusl was not sufficient. Therefore, you must repeat that ghusl and not perform ghusl in the future until you are sure that you have become totally pure. Besides, according to the view of the majority of scholars, you must make up for the prayers that you performed without ghusl. There is a difference of opinion regarding making up those prayers but in order to be on the safe side, it is better to make up for them, pursuant to the view of the majority of the scholars.

You should not perform ghusl before making sure that you have become pure, and you should not delay performing ghusl after making sure of seeing purity; rather, you should hasten to perform it so that you do not abandon any prayers or leave them until their due time is over.  

Allaah knows best.