Do light yellowish, dough-colored discharges at the end of menstruation constitute the "white discharge" (al-qassah al-bayda') that necessitates ghusl?

The "white discharge" is a white fluid unmixed with any yellowishness. If it is mixed with yellowishness, it is not considered part of it. If you do not see the white discharge, then the sign of purity is dryness, meaning inserting a cotton swab and it coming out clean, at which point ghusl (ritual bath) becomes obligatory. Yellowish discharges connected with blood are considered menstruation. What comes from it after purity is not menstruation. If the yellowishness is continuous such that you do not see dryness after the blood stops, then it takes the ruling of istihadah (irregular vaginal bleeding), and ghusl becomes obligatory immediately after the blood stops, along with performing ablution for each prayer when its time enters.