Unfortunately, since the Alpinas farmed out to Borrani were not BMW parts, there are no BMW caps to fit. Proper caps do show up for stupid money on German eBay from time to time. If you want to know what they're supposed to look like, drop me an email and I'll send some photos. Once my own Borranis get to the top of the "do" pile, I'm going to either have some made or follow some internet leads for reasonable facsimiles.
Two of my Borranis still have original paint on them and it's a hard color to describe. It's not silver. More like a warmish grey (less brown than Sahara) with a very (very) slight amount of metallic flake. I don't have the wheels here in VA (they're at my brother's house in CT) and I don't have photos, but I'll see what I can do. Otherwise, if you're in or around Wethersfield CT, you're welcome to go have a look at them or borrow them to take to a painter for a match.