All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
These brown discharges or spots which you have before the menses are not menses. Umm 'Atiyyah said: "(After we used to become pure), we never considered the yellowish or muddy-colored discharge to be impurity." [Al-Bukhari] Moreover, 'Ataa' said: "The muddy and yellowish discharges during the days of menses are considered menses." Furthermore, Sufyaan said: "The yellowish and muddy discharges during the days of menstruation are considered menses. However, the blood, the yellowish and muddy discharges which a woman sees after the days of menses, they are considered bleeding [discharges] outside the monthly periods." This means that the ruling which applies to a woman during this period is that of a pure woman in regard to permissible things and obligations. Nonetheless, she is obliged to clean her private parts from the yellowish and muddy-colored discharges as these invalidate ablution. However, if there are signs which indicate that what she has seen are menses, like if a woman has these discharges immediately before her monthly periods and are connected to it, and she feels the pain of regular menses, like pains in the back and the like, that usually happen during menses, then she is in menses.
For more benefit, please refer to Fatwa 83454.
Allaah Knows best.