The paper presents a freeform metasurface color router designed to achieve ultracompact pixel sizes and overcome the efficiency limitations of conventional color filter-based image sensors. The metasurface is optimized using a fully differentiable topology optimization framework to maximize design space utilization while ensuring fabrication feasibility and robustness to errors. The device can distribute an average of 85% of incident visible light according to the Bayer pattern with a pixel size of 0.6 μm. The metasurface's performance is validated through numerical simulations and experimental measurements, demonstrating higher signal-to-noise ratios and energy efficiency compared to conventional color filter-based systems. The study also discusses the design methodology, optimization process, and practical applications, highlighting the potential for advanced photonic device design and high-resolution image sensors.The paper presents a freeform metasurface color router designed to achieve ultracompact pixel sizes and overcome the efficiency limitations of conventional color filter-based image sensors. The metasurface is optimized using a fully differentiable topology optimization framework to maximize design space utilization while ensuring fabrication feasibility and robustness to errors. The device can distribute an average of 85% of incident visible light according to the Bayer pattern with a pixel size of 0.6 μm. The metasurface's performance is validated through numerical simulations and experimental measurements, demonstrating higher signal-to-noise ratios and energy efficiency compared to conventional color filter-based systems. The study also discusses the design methodology, optimization process, and practical applications, highlighting the potential for advanced photonic device design and high-resolution image sensors.