foreground/background of a push-button?

As push-button is a subclass of simple-pane, I would have expected the
initargs :foreground and :background to have an effect (section 3.1.2
of the capi user's manual).  However, they do not appear to change the
behavior from the default black foreground and the battleship grey
background. 

Am I missing something?

Thanks,

-Scott D. Kalter

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(use-package 'capi)

(contain (make-instance 'push-button
                        :foreground :blue
                        :background :red
                        :text "foo"
                        :min-height 45
                        :callback #'(lambda (&rest args)
                                      (display-message "test"))))