Marks with similar-looking letters (F and E) in light colors look bad on white background (hard to notice). Use contrasting darker colors (if at all) and more distinct text labels, maybe also bolded.
I suggest small graphical icons (~16x16) with distinctive colors and sillhouetes. Maybe:
A gray X over a black dollar sign for Free
A green exclamation mark for Easy
A yellow yield sign with an exclamation mark for Memetic Hazard (like your lightbulb one, but probably a lightbulb shape would be too small to make out at reasonable icon size).
It would also be good to arrange the icons and entries in a table, so that a given icon always appears in the same column.
Marks with similar-looking letters (F and E) in light colors look bad on white background (hard to notice). Use contrasting darker colors (if at all) and more distinct text labels, maybe also bolded.
I changed the colors. I will think about some other form of labeling.
I suggest small graphical icons (~16x16) with distinctive colors and sillhouetes. Maybe:
A gray X over a black dollar sign for Free
A green exclamation mark for Easy
A yellow yield sign with an exclamation mark for Memetic Hazard (like your lightbulb one, but probably a lightbulb shape would be too small to make out at reasonable icon size).
It would also be good to arrange the icons and entries in a table, so that a given icon always appears in the same column.