Sembra che la modalità di alternare i colori sia già stata implementata
da qualcuno e si chiama Hicolour:
da:
https://en.wikipedia.org/wiki/ZX_Spectrum_graphic_modes
(...)
"8x1" attributes
On other Spectrum models, this effect can be replicated by exploiting
the fact that the ULA re-reads the attribute information on every pixel
row when generating the video output; it is possible to write a new
value to the relevant memory location in between successive lines, and
thus cause a different pair of colours to be shown. However, the
Spectrum's processor is not fast enough to write to an entire row of
attribute bytes in one scanline, so 8×1 attributes can only be achieved
over 18 columns. This technique is variously known as Hicolour,
Multicolour, FLI or Rainbow
