Highlighting a single character with syntax coloring

Questions & Answers
1

For a custom drracket color scheme, is there any way to color a single character anywhere in the editor regardless of where it is?

2

I don't think there's a way to highlight a single character. DrRacket colors the program by tokens using #lang-provided lexer, so the colorer doesn't even see characters.

3

Seems not possible in Racket editor, but in Emacs yes (i already have the config) : if you high light syntax for a string it does not need to be a space or tab isolated token, for example if i high light TODO in color then the TODO? string will still have TODO in color.So i suppose you can color a single character string too.

TODO is a string of char being a token in color :

Capture d’écran_2026-10-07_12-11-13
Capture d’écran_2026-10-07_12-11-131435×169 19.7 KB

TODO is a string of char not being a token but still in color :

Capture d’écran_2026-10-07_12-27-51
Capture d’écran_2026-10-07_12-27-51692×218 16.7 KB

this could be done in emacs with this config in .emacs :

(font-lock-add-keywords 'scheme-mode
  '(("\\<\\(TODO\\)" 1 font-lock-warning-face prepend))) ;  case sensitive !

Instead of TODO you can test with a single string char of what you want.