Everything seems to work fine. Luckily the charger has an overload state where it shuts itself off, so it was probably only on for a few seconds. I'd hate to imagine what would have happened otherwise.
My negative cable is definitely red. Looking closely it does have a "-" indicator, but all I saw was red (no pun intended). I've never seen the colors reversed like that. Seems a bit unsafe. I thought black and red were the universal - and +. If mine were black and black I would have at least taken a closer look, but having them reversed like that is a recipe for an accident. Weird.
FWIW at this point, that 'red' cable is really the German version of brown, which they use for ground. Unless yours is bright red...
It is certainly possible that you may have done some damage - how long was it hooked up? Have you tried it to see if it still works?
You are wearing goggles or some sort of eye protection while you do this, right?