From Halopedia, the Halo wiki
Camouflage cloaks are devices employed by the UNSC as a medium of concealing its soldiers in certain environments. Though crude by the standards of the Covenant's active camouflage technology, the camouflage cloak still gives humans an advantage.
The camouflage cloak can be worn over most armors, including advanced suits such as MJOLNIR armor. These cloaks not only contain passive camouflage patterns to fool inattentive enemies, the cloak also masks the thermal signatures of the wearer to avoid detection.
Similar technology, photoreactive panels, was physically integrated into the SPI armor, an armor system used by members of the SPARTAN-III Program, as well as UNSC Prowlers in form of texture buffers.
List of appearances