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Colloidal crystals can exhibit distinct structural colours that resulted from incomplete photonic bandgap. In this Letter, two kinds of colloidal crystals are fabricated and used to realise tunable colour by changing lattice distance and refractive index contrast between the particles and the medium among the particles. Through experiment and simulation analysis, the stop band characteristic of colloidal crystal is affected by the refractive index contrast and the lattice distance. The shift of peak position is nearly linear to the lattice distance even if the refractive index contrast is different. Longer tunable colour range and narrower bandwidth can be obtained in the colloidal crystal with lower refractive index contrast. Colloidal crystal with lower refractive index contrast has lower reflective intensity. The peak intensity is also related to lattice distance and there is an optimal lattice distance where colloidal crystal can obtain highest peak intensity. Such an investigation can help to acquire nice tunable colour by changing the stop band characteristic on the colloidal crystal.