I make Ghusl in the last day of menses but still some exudates appear which are dark red to black in color. Should I make Ghusl again or not?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

It seems from your question that exudates which appear between dark blood and pure white cotton constitute menses. So, you have to abandon the prayer and fasting during such a time.

It is reported in Al-Bukhari that women would send to 'Aa’ishah small boxes with yellow-stained cotton, and she would tell them. “Do not be in haste until you see the pure white cotton.”

Thus, you have to perform Ghusl again after complete purity which you may recognize without any trace of blood nor muddy color.

Here, a woman will see a white pure fluid coming out of her vagina. So, you must not be in a haste until you find such a state of purity.

Allah knows best.