Praise be to Allah.
The ongoing discharge that comes out of woman is taahir (pure) according to the most correct of the two scholarly opinions, but it invalidates wudoo’ and the woman who has this problem must deal with it like urinary incontinence, so she should do wudoo’ for each prayer and pray whatever she wants of obligatory and naafil prayers. You will find more details on that in the answer to question no. 50404.
A woman may know that her period has ended by one of two signs:
1 – Emission of the white discharge.
2 – Complete dryness, such that if she inserts a piece of cotton it comes out clean with no trace of blood or yellowish or brownish discharge on it.
al-Baaji said in al-Muntaqa: The usual sign of tuhr (end of the period) is two things: the white discharge or dryness, which is when a woman inserts a piece of cotton or cloth into her vagina and it comes out dry with no trace of blood on it. Women’s usual patterns with regard to that vary; some of them see the white discharge and some see the dryness. End quote.
If the yellowish or brownish discharge comes immediately after the period then it is part of the menses. If it comes after the tuhr has been established, then no attention should be paid to it.
Al-Bukhaari (may Allaah have mercy on him) said in his Saheeh: Chapter of the coming and going of menses; the women used to send to ‘Aa’ishah vessels containing pieces of cloth on which there were yellowish marks and she would say: Do not be hasty until you see the white discharge, meaning thereby the end of the menses (tuhr).
The colour of menstrual blood usually changes towards the end of the period, and becomes lighter in colour, and it may be followed by a yellowish or brownish discharge. The report of ‘Aa’ishah (may Allaah be pleased with her) indicates this, and indicates that the yellowish discharge that is connected to the period is regarded as menses.
The basic principle is that you should regard this yellowish discharge as part of the period, not spotting, so long as you have not ascertained that the period is over, especially as you see the brownish discharge after doing ghusl. This makes it more likely that it is menses.
But if the end of the period is ascertained by seeing the white discharge or complete dryness, then you should not pay any attention to the yellowish and brownish discharge in that case. This is what is indicated by the words of Umm ‘Atiyah (may Allaah be pleased with her): We used not to regard the brownish and yellowish discharge after the tuhr (end of the period) as being of any significance. Narrated by al-Bukhaari (320) and Abu Dawood (307).
And Allaah knows best.