One of the wives of Messenger of Allah ﷺ practiced Iʿtikaf with him while she ad bleeding in between her periods and she would see red (blood) or yellowish traces, and sometimes we put a tray beneath her when she offered the prayer. (Using translation from Bukhārī 2037)  

«اعْتَكَفَتْ مَعَ رَسُولِ اللهِ ﷺ امْرَأَةٌ مِنْ أَزْوَاجِهِ مُسْتَحَاضَةٌ فَكَانَتْ تَرَى الْحُمْرَةَ وَالصُّفْرَةَ فَرُبَّمَا وَضَعَتِ الطَّسْتَ تَحْتَهَا وَهِيَ تُصَلِّي»