All-dielectric metasurface (ADM) color filter arrays (CFA) are attractive for replacing conventional organic-dye color filters due to several advantages such as CMOS-compatibility, size scalability, and robustness to degradation. We propose metasurface designs with polygon-shaped unit cells for improving the performance of such filters. Our numerical results predict improvement in color purity for red, green, and blue primary color filters and significant reduction in insertion loss for blue filters as compared to the previously reported designs using simple circular shapes. The proposed differential evolution optimization methodology can be useful for improving the performance of other metasurface spectral filtering structures.