Controlling and understanding the assembly of colloidal nanoparticles remains a challenging issue for optimizing magnetic-plasmonic devices for various applications including sensors, displays, bio-imaging, and therapy. A magnetic field is successfully utilized to induce the fabrication of multidimensional structures composed of magnetoplasmonic (MagPlas) particles, which exhibit interesting optical properties. Notably, a magnetic-field assisted coating technique for fabrication of two-dimensional (2D) amorphous photonic crystal (APC) film of the MagPlas particles on a filter membrane is proposed. The MagPlas 2D APC exhibits strong dual reflected colors caused by structural scattering and plasmon resonance scattering. The water absorption ability of the membrane and the high refractive index sensitivity of plasmon resonance scattering are utilized to fabricate a simple colorimetric humidity sensor. Additionally, a mechanical colorimetric sensor that instantly exhibits responses to both bending and stretching forces is fabricated by embedding the 2D APC film into PDMS substrate. Because of unique features including dual-color characteristic, flexibility, and high plasmonic sensitivity, these kinds of the platform could be highly promising as wearable devices for physical, chemical and biological sensing with naked eye detection.