This week, Apple decided to discontinue the space grey Magic Mouse 2, Magic Keyboard and Magic Trackpad with all three products still being listed for sale, but like it did with the HomePod the product listings say: “While supplies last”, in pretty small text. The iMac Pro was discontinued back in March this year and the discontinuation of these accessories is likely due to that.
Apple only launched these accessories alongside the iMac Pro in 2017 and for a while, they were only available to purchase with that computer which created an eBay rush at the time. Later on, Apple did start selling all three separately at a price premium to the standard silver ones. The silver Magic Mouse is £79 / $79 and the space grey ones are £20 / $20 more, for some reason.
Apple is offering new colour options for the new M1 iMac, which was announced last month. Each option comes with a keyboard in the same colour as the iMac, as well as a mouse and or trackpad. Apple isn’t currently offering each colour accessory severalty, however this could change.