Within the theory of light reflection by nonabsorbing substances the results of computer simulation of optical effects in polytwin crystal structures are discussed. A consideration is given to the problem of optimal observation conditions for crystal domains and polytwin plates with the help of reflective anisotropic contrast effect. A special attention is paid to ferromagnetic polytwin crystals. The interpretation of their domain structures is shown to demand taking account of superposition of anisotropic reflection and Kerr magneto-optical effects.