Fuse - the Free Unix Spectrum Emulator

The standard Fuse code has a 16 colour palette in each UI corresponding to
the standard Spectrum colour scheme (e.g. for SDL colour_values[]). The
proposed ULA+ has a fixed 256 colour palette instead (with up to 64 colours
"active" at one time), so this could be supported by extending e.g.
colour_values[] to 256 entries for the full palette of the ULA+.

The ink and paper arguments to uidisplay_plot8() are indexes to the above
array, so uidisplay_plot8() would not need to be otherwise modified to
handle plotting in all the ULA+ colours. The code that maps the attribute
to a colour index in the above array in display.c display_parse_attr()
would need to be aware of the CLUT indexes. I'd suggest making this
function a function pointer like the flashing function (see
display_dirty_flashing_fn in display.h).

I don't quite see what you mean, maybe you can give me a few more
pointers?
I was not happy with having to replace uidisplay_plot8, but it was the
only way I could think of making it work, as I am not familiarized with
FUSE's source code.
I'd like to add this feature with as little changes to FUSE as possible,
so I'll rework the code according to your indications.

The ULA+ has a fixed 256 colour palette, I'd suggest that should just be
assigned in each UI instead of the existing 16 colour palette and then you
could use the existing uidisplay_plot8 to draw pixels.
clut_update_palette() would also then not be required.