It's like a trippy and visually spectacular 3D kaleidoscope or something. The cyclists are wearing a LED light suit that can change colours and the flash-rate and the luminosity so that they can look completely different while they spin around in carefully choreographed moves.
Called Ghost Peloton, it was created by NVA and the Phoenix Dance Theatre for the grand depart of the Tour de France 2014. NVA writes:
Ghost Peloton fuses performance cycling with athletic choreography performed by Phoenix Dance Theatre's dancers, and the varied landscapes of race route. Each rider, bike and performer was illuminated using NVA's bespoke LED light suit, which can instantaneously change colour, flash-rate and luminosity. The rhythm of movement from the choreographed actions of massed participants becomes a source of creativity in itself, extending perception of the immediate setting.