sorry but i gotta bump?
Actually I believe the real reason filters are generally black is so that algae doesnt start to grow in the filter mucking everything up. The bacteria are not photosynthetic, thus do not require light, nor are they harmed by light.I'm pretty sure that the bacteria in your filter is the same as the bacteria in your gravel, so I can't imagine that light hitting it would kill it....... (could be wrong) But I'm also fairly certain that most filters are made of black plastic 'cause most people don't wanna see the icky muck in their filters.