Bright Chao are shiny two-tone Chao from the HD remakes of Sonic Adventure 2. However, due to a porting glitch, their appearance seems to be very bright - hence the community nickname "Bright Chao". Other nicknames given are names such as "Neon Chao" or "Luminescent Chao".
Bright Chao usually appear all white with little to no visible highlights. However, when the Bright Chao is a dark type, you can start to see their colours and only their highlights appear bright.