Highlighting newline chars is trivial using the library
highlight-chars.el
:M-x hc-highlight-chars C-q C-j RET font-lock-comment-face RET
You are prompted for the chars to highlight -- hit
C-q C-j
(inserts a newline char), then hitRET
to enter the list of chars you inserted (just a newline char here).You are then prompted for the face to use to highlight those chars (in this case, just one char, newline) -- type
font-lock-comment-face
or whatever other face name you like.See description of the library here.
And if you want to also change the display to show (the highlighted char) ¬, then just do also what you already tried:
M-: (standard-display-ascii ?\n "¬\n")
The result of #1 + #2 is highlighted ¬
in place of the usual newline display.