Mechano-responsive photonic hydrogel is fabricated through an efficient magnetic assembly method. This hydrogel film exhibits ultrafast color switching (Δλ/t=~1.2 nm/ms) across a broad wavelength range (Δλ =~250 nm). The mechanochromic sensitivity is Δλ/σ=20–40 nm kPa−1 in touch pressure region. The hydrogel can be applied for simultaneous multicolor display.