I'm only seeing Fireworks fountain grass on a Google search, and there's a Pennisetum 'Fireworks' in the ATP database. Is that it? They're only listed as hardy to Zone 9 or warmer outdoors so in your zone you'd need to bring them indoors if you want to keep them over winter. I have grown other fountain grasses and they've been very intolerant of frost, which makes the foliage go brown and dead, as does getting too dry. You may be able to save the one with the dead top if the roots are still alive. Cut off the dead stuff and keep both containers from freezing would be my suggestion.
