or dynamic reflection spectral measurements. [18,19] The colors of the PhCs are related to a wide range of changes in the physical properties of the materials forming the photonic structures rather than specific chemical states responsible for absorption in a characteristic wavelength region. [20] Hence, the materials for fabricating PhCs have no specific chemical requirements. Regardless of its chemical properties, any material with a photonic structure can display iridescence as long as the PBG is located in the region of visible light wavelengths, which leads to the potential for broad applicability in colorimetric response.As an important technical extension of responsive PhCs, magnetically tunable photonic systems have been developed through the self-assembly of uniform superparamagnetic colloidal particles in liquid media, [21][22][23][24] which provide a new platform for chromatic applications. The magnetic fields in these systems play a vital role in color modulation, with the benefits of contactless control, instant action and ease of integration into electronic devices. However, the colloidal stability of such systems is poor due to the chain aggregations of dynamically ordered assemblies induced by the magnetic packing force. [25][26][27] Using a polymer matrix to stabilize the photonic structures is an ideal way to stabilize the diffraction color. Nevertheless, the magnetic field-responsive chromic capability will disappear because the ordered array structure is fixed by a polymer net. Consequently, considerable effort has been devoted to realizing color displays of polymers or hydrogels based on magnetic photonic chains exposed to various external stimuli. Many researchers have experimented with the manipulation of humidity with a saturated salt solution to drive color changes in magnetic polymers. [28][29][30] Other researchers have investigated the thermochromic display of magnetic hydrogels by changing their temperature with a water-bath control system. [31,32] However, nearly all of these previously explored stimuli require physical contact with the polymers or hydrogels, which may limit their applications. Therefore, new approaches for color displays of solidified magnetic polymers or hydrogels that operate in a contactless way are still anticipated.In this work, we develop a novel approach for magnetochromic displays with a solid magnetic photonic hydrogel. Color switching is initiated by an alternating magnetic field As an external stimulus for stimuli-responsive chromic materials, a magnetic field has the benefits of contactless control, instant action, and ease of integration into electronic devices. Hence, the development of a magnetically responsive photonic crystal provides a new platform for color displays. However, magnetically controlled display systems have been primarily limited to liquid systems of colloidal crystals; their application to solid chromic systems has been difficult because the ordered array structure is fixed by a polymer network. A novel solid magnetochromic photonic ...

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