Special enhanced silver mirror coatings were designed and fabricated to minimize the polarization introduced by a three-mirror off-axis high-accuracy telescope. A system diattenuation of approximately 1% in the VIS-NIR was achieved by both reducing the diattenuation from each mirror individually and by balancing the diattenuations introduced by the three mirrors over the spectral range. This process of low-polarization engineering involves minimizing system polarization introduced by surface geometry, thin film coatings and birefringent elements, and measuring the system. In this report we will outline a methodology to minimize instrumental polarization aberrations, with an emphasis on achieving low diattenuation in the MSPI camera, given its off-axis geometry and coating design constraints imposed by the space-based application. This polarization balancing technique for mirror coatings can be applied to astrophysics applications.