Confused when setting an Emacs face

Question

(set-face-attribute 'diredp-dir-heading nil '(t (:foreground blue :background dark1)))

What should be the right statements to set this face? Bow//

Answer 1

Face attributes :foreground and :background must have string values.

So try "blue" instead of blue etc.

The error message you see is saying that you asked Emacs to evaluate blue, which means find its value as a variable. Emacs tried that and found that the symbol blue has no value as a variable. The string "blue", on the other hand, evaluates to itself, and a string is exactly the kind of value that is needed here.