You can always find the white or silver ( which you will never use ) at your regular home depots and Lowes, but black is quite difficult to find and I had to buy a case of it to get any. I still have a number of sheets if you would like some, but I have had trouble with filament algeas growing more on the black. I cant explain why. If you are in need you can pm me, but I'm not on often so the best way is to email me at email@example.com.
I actually have no idea. I have tried putting in tangs to mow it down but it still comes back. I have spoken to another friend who has had the same issue. I don't know the black absorbs all the light and heats more than the other ambient structures to cause increase growth or what, but I have pulled it.