In no particular order:

• "local", "return", "repeat", "until", "goto", "break", are not highlighted as keywords.
  – Lua' block comments (--[[ text --]]) are supported but not highlighted accordingly.
  – Underscore "_" is in the "symbol group" (white) while it shouldn't be.
• Dot "." is not in the "symbol group" while it should be.
• Consider highlighting strings in the same colour as numbers (currently highlighted as "identifiers").
• Consider highlighting built-in function and constant names in a distinct colour (e.g. peach).
  – If it is not overly technically challenging, consider disabling the cursor flashing when the pico-8 window is not in focus.
  ~ Not about the code editor itself, but in the context of the quite so limited window width and existing shortcuts, it could be worth to look into adding a "func" alias to the "function" keyword. (update: no longer needed for size concerns, only for use with editor)
  – Quickly tapping Up,End or Down,End causes the editor to shift the cursor position by two lines instead of placing it at the end of the previous/next line.
  – Consider permitting insertion of semicolons via the editor. Lua manual suggests the use of semicolons for some constructions to avoid the parser from accidentally "gluing" multiple unrelated statements together.

Should probably be merged with this thread.

As per 0.1.1:
– "in" should also be in keyword group.
~ Maybe "true"/"false"/"nil" should be in some group.
– if an identifier starts with an underscore "_", the underscore is highlighted as a symbol.
– "seed" is highlighted as a function (but it isn't) while "srand" isn't (but it is)

Having caps-lock on while using the CTRL+F search feature inputs invisible or weird characters. (not that you ever need caps-lock on - I just noticed once when I accidentally had it on)

– ".." counts as two tokens ("..." probably should also be one token)
– "sub" is not highlighted as a function