One of the very kind proof readers raised the issue of colour blindness and how it might relate to my topos. Originally I planned to use white lines (with various dots and dashes to distinguish lines that overlapped) but I felt they weren’t clear enough so started using a mix of white and red or green (which I used depended on the colour of the background) dashed lines.
So I have redrawn one topo in four different ways to see which is most effective.
1. Red and white dashed lines
2. White dashed lines with a black background.
3. White dashed lines.
4. White solid lines.