What should you do about the appearance of light brown traces after performing ghusl and fasting for several days of Ramadan, and is fasting the last two days valid?

If a woman's customary period is six days, and she sees purity after five days, she should perform ghusl, pray, and fast. If bleeding recurs after her customary period has passed, and the blood is not suitable to be considered menstruation (less than a day and a night), then it is not to be given any consideration. Likewise, brownish discharge (kudra) after the customary period is not to be given any consideration.

Based on this, the few light brown traces that the questioner saw, which lasted less than a day and a night, are not to be given any consideration. Her fasting on the third and fourth days of Ramadan is valid, and she is not required to perform ghusl for that brownish discharge.