get-color-from-user in Dialogs

• (get-color-from-user message parent init-color style) -> color% object or #f
   message = #f : string or #f
   parent = #f : frame% or dialog% object or #f
   init-color = #f : color% object or #f
   style = null : an empty list of symbols

  Lets the user select a color though the platform-specific (modal) dialog, using parent as the parent window if it is specified. The message string is displayed as a prompt in the dialog if possible. If init-color is provided, the dialog is initialized to the given color.

  The style argument is provided for future extensions. Currently, style must be the empty list.

  The result is #f if the user cancels the dialog, the selected color otherwise.