The time dependence of optical density during a coloration and bleaching sequence has been investigated in the isotropic phase for several liquid‐crystalline materials doped with a small amount of tetra‐n‐alkyl‐ammonium iodide. As a result, a rate equation fitting experimental results obtained for low current densities has been derived:dOD/dt=&agr;J−&kgr;(OD+OD0), whereODis the change in optical density of colored cells after the application of dc current,Jis the applied current density, &agr; is a coefficient related to the coloration rate, &kgr; is a coefficient governing the bleaching rate, andOD0is a constant for a given cell. Furthermore, the dependence of these coefficients upon electrolyte concentration, cell thickness, and cell temperature has been studied. The value of &agr; is almost independent of device parameters, while &kgr; is dependent upon the latter two parameters.