Polyelectrolyte porous membranes (PPMs) have numerous applications in modern science and technology. Here, we describe a new platform for creating multifunctional supramolecular PPMs (SPPMs) by cross-linking of single-component homopoly(ionic liquid)s (PILs) containing hydrophilic anions (Br–, MBry–, M = Sn, Pb, Sb, Bi) with H2O molecules. With a range of experimental evidence and support from theoretical calculations, we show that the porous architecture is formed by H2O molecules-induced phase separation of the polycationic moieties of the homo-PILs between their polar and apolar domains, which are cross-linked together by multiple hydrogen (H)-bonding interactions. Furthermore, we discover these SPPMs show reversible, dynamic, wide-range color tuning, depending on the excitation wavelength, as well as ultrasensitive color change toward humidity and temperature stimuli, endowing them with great promise in color-on-demand applications. These findings, together with the scalable and green synthetic approach, bode well for advanced membrane materials and color-on-demand applications based upon such SPPM systems.