[en] Highlights: • The volume of CH₃NH₃Pb(I_1−xBr_x)3 decreases linearly with the concentration of Br ions. • Theoretical calculations show that the color of crystal can be tuned from wine to yellow by controlling the concentration of Br ions. • The relationship between the absorption spectrum and crystal color has been discussed. Chemically tuned inorganic–organic hybrid halide perovskites based on iodine and bromine halide anions have been studied using first-principles calculations. Firstly, our results show that the volume of ${\mathrm{CH}}_3{\mathrm{NH}}_3\mathrm{Pb}{({\mathrm{I}}_{1-x}{\mathrm{Br}}_x)}_3$ decreases linearly with the concentration of Br ions, and the band gap can be tuned from 1.9 eV to 2.3 eV by substituting I with Br, resulting in the shift of absorption onset from 650 nm (1.9 eV) to 540 nm (2.3 eV). Secondly, our calculations show that the color of crystal can be tuned from wine to yellow by substituting I with Br.