We report on the tailoring of detection bands of InAs quantum-dot infrared photodetectors (QDIPs) using InGa1-xAs capping layers and on the realization of voltage-tunable two-color QDIPs for mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) detection. QDIPs having 2.0 ML InAs QDs capped by 20 ML In0.15Ga0.85As layer show bias-dependent photocurrent peak positions in the LWIR regime (similar to8-9mum) which are redshifted with respect to those (similar to5-7 mum) in the counterpart QDIPs without InxGa1-xAs capping layers. QDIPs having 2.5 ML InAs QDs capped by a 30 ML In0.15Ga0.85As layer have a bimodal QD size distribution and show voltage-tunable MWIR (similar to5.5-6 mum) and LWIR (similar to9-11 mum) photoresponse. At low bias, MWIR photoresponse is dominant whereas with increasing bias, the LWIR photoresponse becomes dominant.