What is the adopted view regarding yellowish and brownish discharges during the period of purity: Are they impure and invalidate ablution, or pure and invalidate it, or pure and do not invalidate it, given the disagreement among muftis and the questioner's trust in their knowledge and piety?

Yellow and brownish discharges are impure (najis) and invalidate ablution (wudu'). They are not like "vaginal discharges." No recognized jurist (faqih) has ever deemed them pure, except for Ibn Hazm, who held that they do not invalidate ablution, but this opinion is considered anachronistic (shadh).