How to defeat the fontification of colour literals in css-mode?

Question

Emacs css-mode is fontifying my colour literals. For example:

This makes the text harder to read.

I tried to defeat it with the following in my .emacs. (Note: this matches on ‘hsl’ because those are the only literals I actually use.)

(font-lock-add-keywords nil
 '(
   ("color: *\\(hsla?(.*)\\)" 1 'default t) ; Colour literal
   )
 )

This fails. I can override the fontification of other things, but somehow these colour literals are override proof.

How can I defeat this unwanted fontification?

Answer 1

M-x customize-group RET css RET

would inform you about:

C-hv css-fontify-colors

css-fontify-colors is a variable defined in `css-mode.el'.
Its value is t

  This variable is safe as a file local variable if its value
  satisfies the predicate `booleanp'.

Documentation:
Whether CSS colors should be fontified using the color as the background.
When non-`nil', a text representing CSS color will be fontified
such that its background is the color itself.  E.g., #ff0000 will
be fontified with a red background.

You can customize this variable.

This variable was introduced, or its default value was changed, in
version 26.1 of Emacs.