just one thing (sorry saying, all people that had a zx-spectrum can spot it in a second...): on a zx-spectrum (using the default ula) you can't have bright 0 and 1 colours simultaneously in the same 8x8 pixel cell (like your picture shows on cyan and yellow, and that bright yellow on dark blue) - see the "colour attribute area" from http://www.breakintoprogram.co.uk/computers/zx-spectrum/screen-memory-layout (it's 768 bytes long, located between 0x5800 and 0x5AFF) - for verifying, just try to open the picture on zxpaintbrush (resizing it to 256x192 of course! ;) ) or multipaint (resizes it automatically)