For example, if the code said
it would appear as
giving this sort of effect:
This is to do with colouring in font-lock-mode; the Foo is displayed in font-lock-constant-face which is set by default to “dark cyan".
The change in Emacs appears to be that if it doesn't recognise the face it displays in background (white), whereas before it used to display in black; resulting in white-on-white.
The fix is to change the face to something that Emacs does recognise, for example “cyan4”.
- In Emacs, put point on an area of invisible text.
- From the menubar (which may be subtly different on other operating systems, of course), select Options > Customize Emacs > Specific Face...
- The Minibuffer should say “Customize face (default `font-lock-constant-face’): ”; press Ret.
You should now see something like
Change the “dark cyan” to “cyan4” - or whatever colour takes your fancy - and press Set for current session, to test it out on your code, then Save for future sessions to keep the setting.