I thought scarlet badis and dario dario were the same.
When I saw the rainbow badis at HFF some had exactly the same colouration as my belated scarlet badis and some were much paler but perhaps a bit of iridescent sheen. They looked rather like a scarlet badi that has lost it's colour, maybe due to being the least dominant male. They were exactly the same size, shape etc as what I know to be a scarlet badis, as seen the link in Zev's post.