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.
Face attributes
:foregroundand:backgroundmust have string values.So try
"blue"instead ofblueetc.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 symbolbluehas 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.