Recent Scintilla versions have support for displaying e.g. CR/LF in a different colour.

Search https://www.scintilla.org/ScintillaDoc.html for SC_REPRESENTATION_COLOUR and SCI_SETREPRESENTATIONCOLOUR

It would be great if this feature makes it into N++ as well.

Some messages on the Scintilla mailing list:
https://groups.google.com/g/scintilla-interest/c/-zLNwzJ18Q4/m/EZfyqGEaAQAJ
Not sure whether this is related. The search engine finds it if one searches for the SC_/SCI_ constants, but I don't see why:
https://groups.google.com/g/scintilla-interest/c/g1Ypo8qijJU/m/o9zZCGSSAAAJ

The now closed feature request for Scintilla: https://sourceforge.net/p/scintilla/feature-requests/1129/