The chameleon doesn't control the transition. His nervous system autonomously does the job ...

I have not read the research work which is published in Nature Comm. However, one can use common sense to conclude that the mechanism responsible for the this change in colour is due to a set of micro-sized prism ( may be nano-prism to have very intense and bright colour) that rotate through different angles to produce different colour depending on the signals coming from the nervous system ( the brain). I think just ordinary light can do the job and not infra-red.I mean one can produce different colour from a prism exposed to sunlight.