Simplify flat-color 3D models fast using automated polygon reduction tools that preserve color edges—such as Blender’s Decimate modifier (Planar mode) or Meshlab.
These tools remove non-essential vertices without breaking the distinct color boundaries critical to flat-color designs. Prioritize "Planar" or "edge-preserving" modes—they’re built to maintain the clean, blocky look flat colors depend on.
For Blender users: Start with the Decimate modifier set to "Planar" (faster for flat surfaces) and tweak the "Angle Limit" to keep color edges sharp.