Eh?
My Windows 7 is already 32-bit 1080p.
My WinUAE config for Workbench is A4000/060 with AGA at most. How am I supposed to get more colours from Workbench?
Eh?
You're running WinUAE, you're not limited to standard Amiga screenmodes (i.e., AGA).
Emulate a 16-bit or 24-bit screenmode to increase you're color depth and see if it gives you smoother gradients. If I understand correctly from your picture of the color palette wheel, that's what you think you're missing, yes?