In this paper, we present a physics-based full three-dimensional (3-D) numerical simulation of simultaneous two-color medium-wave infrared long-wave infrared (MWIR-LWIR) and LWIR-very-long-wave infrared (VLWIR) detectors. The present approach avoids geometrical simplifications typical of one- or two-dimensional models that can introduce errors which are difficult to quantify. We include all the relevant material physics and the drift-diffusion equations are solved on a 3-D finite element grid. We simulate device structures that have been fabricated and characterized for operation in the MWIR-LWIR spectral regions and compare the numerical results with the measured values. Furthermore, we apply the same model to predict the performance of similar detector structures intended for operation in the LWIR-VLWIR spectral regions.