LUMATIV have a line of LED illuminated snapback caps that can change colour, along side a number of motion effects that can also be activated. The electronics is hidden within the cap and can be recharged via a micro USB connector, making the product nicely self-contained. The branding on the caps is currently targeted at sports fans, events and music. It is encouraging to see this type of wearable electronics moving into the mainstream.
Another example of LED in caps is the art piece “photon veils”
Source: Forbes