Your watch 3D model appears darker in physical prototypes mainly because the digital material’s light interaction properties (like reflectivity or roughness) don’t match the real-world material used.
3D models simulate how materials reflect or absorb light—if the prototype uses a less reflective (e.g., matte plastic) or more light-absorbent material than the model’s simulated one (e.g., glossy metal), the physical part will look darker.
Fix this by comparing your 3D software’s material parameters (roughness, metallic values) to the prototype material’s datasheet, or test the physical material under similar lighting to adjust the digital model for consistency.