A dual-wavelength on-axis phase-shifting digital holographic microscopy system based on color CMOS is proposed. Phase variations during the apoptosis process of human jurkat cells (human peripheral blood T cell leukemia) are quantitatively measured and analyzed without complex phase unwrapping algorithm. Using laser with wavelengths of 632.8 nm and 532 nm, color holograms at three states during the apoptosis process of jurkat cells in vitro are then recorded experimentally. Phase of the cells is reconstructed based on the extracted phase information at each wavelength. The experimental results are consistent with the results obtained by other methods. Moreover, the proposed method described here has wide measurement range and it is simple and accurate. The results indicate that dual-wavelength digital holography is a useful tool for research and application of cell phase.