Well you could take my word for it; they are littered around Portsmouth and I often see them go off. Failing that:
Truvelouk.com wrote:
Magenta flash filter for front photography.
http://www.truvelouk.com/installationmains.phtml
Magenta is as a normal camera flash but with the green removed.
The invisible flash 'myth' was probably started because the Truvelo Dcam uses in IR flash, but the Combi SMC (the one we all know and love) is the one approved for UK use (this having the magenta flash). However, new models are about to be released for UK use which do use IR flash.