Does yellowness after blood and before the white discharge count as menstruation, based on legal fatwas, or does it not count as menstruation, based on a doctor's statement?

The correct and authoritative opinion is that if the yellowish discharge (ṣufrah) occurs during the days of menstruation, it is considered menstrual blood (ḥayḍ). There is another opinion held by some scholars that it is not menstruation at all, but this contradicts the view of the majority. Sheikh al-Islam Ibn Taymiyyah held the view that if the yellowish discharge occurs with dark or red blood during the habitual period, then it is menstruation; otherwise, it is not. This is based on the practice of the women companions and the statement of Umm ‘Aṭiyyah: "We did not consider the yellowish or brownish discharge (ṣufrah wa kudrah) after purification to be anything."