It’s a crime to vastly change the UI without leaving an opinion to use the classic colours and icon design from Rhino 7/8.
Rhino 9 UI cheme options:
A. Classic V7 (thin outlines, white accents);
B. Classic V8 (thick outlines, gray accents);
C. Modern V9 (washed-out pastel colours, experimenting with lime green, add eye strain to colour-blind people just for fun).