I can confirm that Powerflex do do a 'black' version to order. I have the black version for the inner springpan bush, but believe me they are unbelievably hard and I haven't fitted them. I just don't like the idea of zero 'give' at all. So I still have the purple ones fitted - these were also shaved down at the sleeve ends to fit, but this was seven years ago, and are still ok. If Powerflex have altered the length of the inner springpan bush, then that's really good news.
I'll try and take a photo of the black version tomorrow and post them on here.