In the Textmode app 
on your Mac, choose Format > Reset Syntax Analysis.
If syntax highlighting doesn’t look correct, first try the following:
In the Textmode app on your Mac, choose Format > Reset Syntax Analysis.
If it doesn’t help, the possible causes include the following:
There is an issue in the text itself, such as invalid programming syntax.
There is an issue in the syntax definition.
Textmode’s syntax analysis cannot determine that part correctly.