Cannot run emacsclient in GUI

["Ramón Lorenzo Panadés-Barrueta" <rpana92@gmail.com>]

Hello everyone,

I have been trying to configure Emacs to have a transparent background when
used in the terminal, and specific background color when used in GUI. For
this I have defined the following hook:

(defun on-after-init ()
  "Make transparent background only for terminal."
  (if (display-graphic-p)
      (progn (message "XWINDOW")
         (set-face-background 'default "#292b2e"))
    (progn (message "TERMINAL")
       (set-face-background 'default "unspecified-bg"))))

(add-hook 'window-setup-hook 'on-after-init)

The above happens to work perfectly for emacs, but not for emacsclient,
which yield the following error:

$ emacsclient -c
Waiting for Emacs...
*ERROR*: Undefined color: "unspecified-bg"

On the other hand emacsclient -nw -c, works as expected. Could anyone
please give me some hints on how to solve this issue?

Thanks in advance.