Is the method of dealing with intermittent bleeding after the first three days considered correct, by performing ghusl and wudu for each prayer, and considering only clear blood as menstruation? And does the discharge of a small amount of blood during prayer invalidate it?

Red blood is undoubtedly menstruation, as long as it occurs within a timeframe suitable for it to be menstruation. The disagreement concerns the yellowish and brownish discharges. You should perform ghusl (ritual bath) when you see purity (cessation of bleeding). If the blood returns, you revert to being in a state of menstruation until it ceases. You may wait half a day or a full day if you know that the blood will return. If the blood and any associated yellowish or brownish discharge cease, then you are pure. If a yellowish or brownish discharge reappears, but it is not connected to blood, then it is not considered menstruation. Performing ghusl and considering yourself pure while blood is flowing during the period of possibility is not correct.