No serious injury thanks - skinned elbow and bruised hip and a bit of a sore neck for a day or two, that's all.
Another rider fell on black ice right ahead of us so we stopped and considered aborting the ride but decided to carry on carefully and as the ride progressed (and the rain started) it warmed up. Later in the ride we met a couple walking their bikes, she looking shocked with blood running down the right side of her face - she had fallen further back on a patch of ice. So we carried on carefully on what was by then a good grippy compact gravel track. Minutes later we met a man, wearing no helmet and only a Barbour jacket, with identical injuries to his face. He said he had fallen on a patch of ice and thought he'd concussed himself because he'd been unable to remember what day it was and wasn't sure where he was staying. We offered to accompany him but he told us he thought he knew where his aunt lived, where he was staying for the holiday. We carried on wondering how bad this ice was going to be and soon after that we found some old slushy water ice across a corner in a dip - not difficult to deal with if you just stayed upright and blasted across as it was all mixed up with gravel.
Back to the shifters: the problem is that this kind of soft plastic actually has its own slightly grainy texture, which it's difficult to reproduce so once you've sanded it, it will always look different. As it's black it reflects light and the texture gives it its tone.