What is Ibn Uthaymeen's opinion regarding the narrations mentioned concerning yellowish and brownish discharges, such as "Do not be hasty until you see the white discharge" and "We did not consider yellowish and brownish discharges to be anything"? And did he weaken the addition of "after purity"?

The final opinion of Sheikh Ibn 'Uthaymeen, which is also the choice of Sheikh al-Islam Ibn Taymiyyah, is that yellowness (صفرة) and turbid discharge (كدرة) are not considered menstruation at all. This is because it is more lenient for women, and it is based on the Hadith of Umm 'Atiyyah: "We used not to consider yellowness and turbid discharge as anything." So, if the bleeding stops for a woman, she should perform ghusl, pray, and fast, even if it is before forty days, or if she experiences yellowness.