I'm not sure of the specifics, but I think Amix shipped with a monochrome-only X server for A2410. I don't know whether the X11R5 server on the Amix 2.1 tape (not installed/used by default AFAIK) is capable of colour.
There are Amix HDFs which have X11R5 and third-party Cirrus Logic card support, there the X desktop is in colour (with Piccolo/Picasso configured in WinUAE). E.g. see
this other post by vintageBytes (use web.archive.org to download that).
Edit: It is possible to use A2410 in colour. Do e.g. "xinit -- -tiga". Not
very colourful but not black & white. [The monochrome-only X server is probably just for native chipset modes.]