[ltk-user] problem with the :background keyword

[harven at free.fr]

Hi,

I am a beginner at both ltk and tk and I am trying to convert a small programme
from Tk to LTk.

Tk version:
pack [button .b -text "Push Me" -background red -command {tk_messageBox -message "hello, world"}]

LTk version:
(with-ltk () 
  (let ((my-button
         (make-instance 'text :text "Push Me"
                        :background :red
                        :command
                        (lambda () (message-box "Hello, world!" "message"
                                                'ok 'info)))))
    (pack my-button)))

The Tk version works fine, whereas the LTk version gives the following error:

  Invalid initialization argument:
    :BACKGROUND
  in call for class #<STANDARD-CLASS BUTTON>.
  See also:
    The ANSI Standard, Section 7.1.2
    [Condition of type INITARG-ERROR]

On the other hand, there is no error if the :background line is removed.
It's as if the :background keyword is only allowed for a few specific widgets,
like the text widget. I also get errors if I try to set it with configure,
as shown in the LTk manual, e.g. (configure my-button :background :blue)

What am I doing wrong ?

Any help is appreciated, I am using tk8.5 on debian squeeze, with sbcl 1.0.55,
and the current release of ltk that ships with quicklisp.
Sincerely,
--
harven