An InAs/GaAs quantum dot infrared photodetector with strong, multicolor, broadband (5-20 μm) photoresponse is reported. Using a combined quaternary In0.21Al0.21Ga0.58As and GaAs capping that relieves strain and maintains strong carrier confinement, we demonstrate a four color infrared response with peaks in the midwave- (5.7 μm), longwave- (9.0 and 14.5 μm), and far- (17 μm) infrared regions. Narrow spectral widths (7% to 9%) are noted at each of these wavelengths including responsivity value ∼95.3 mA/W at 14.5 μm. Using strain field and multi-band k ṡ p theory, we map specific bound-to-bound and bound-to-quasibound transitions to the longwave and midwave responses, respectively. © 2012 American Institute of Physics.