I believe the 9090 doesn’t usually have a red flourish, but this[0] anniversary edition does, and if you look at other Sapper work[1] you’ll see how the red highlight, like the track point[2] seems to fit into a theme of his he works into various products.

[0] https://www.finnishdesignshop.com/design-stories/classic/ale...

[1] https://www.artemide.com/en/subfamily/18869/tizio

[2] https://money.cnn.com/gallery/technology/2015/01/08/thinkpad...