An old post, but I was looking for similar information. I have a spare unpainted Beta alloy wheel which I would like to refurbish to replace the painted alloy spare wheel which has some old rim damage and does not run true. The tyre fitting place could not get it to balance properly when we replaced the ancient, (original delivery tyre), on it with a less ancient one.
My father mentioned to me that when he painted the Lancia Beta wheels years ago by rattle can, he noticed the silver paint finish darkened slightly and lost a little bit of its brilliant gloss finish with each successive coat of clear lacquer finish applied on top of the colour coat. Making it a bit more pewter grey/silver in colour with each new clear coat. So it is possible in theory to fine tune and tone down the finished silver wheel colour if painting by rattle can and applying a clear finish coat or multiple coats.
There is a reference to a Lancia silver metallic #620 colour code here although presumably that refers to a body colour:
https://touchupdirect.com/touch-up-paint/lancia/See also these body colour paint code references:
https://www.uniquecarsandparts.com.au/paint_color_reference_lancia