Is it obligatory to make up the prayers from Fajr to Isha if a woman sees a yellowish discharge before the onset of menstruation, knowing that she had seen a reddish discharge before it, and the yellowish discharge stopped for a period then returned?

If blood reappears after a period of purity, and continues for more than a day and a night, then the first reddish discharge was menses, and the intervening period of purity was valid. Consequently, you must make up the prayers you missed during that period of purity.