Shouldn't custom.el load wid-edit.el?

["Drew Adams" <drew.adams@oracle.com>]

I did this, to let some code work also in older Emacs versions that don't
define type `color':

(defcustom... :type (if (get 'color 'widget-type) 'color 'string) ...)

I was surprised to find that in Emacs 22 also the type was `string'.

The problem was that the widget `color' is defined in wid-edit.el, which was
not loaded. So I now do this, which seems a bit heavy-handed for user code:

(defcustom... :type (if (and (require 'wid-edit nil t)
                             (get 'color 'widget-type))
                        'color
                      'string) ...)

Shouldn't custom.el, which defines `defcustom', load wid-edit.el? How else
can :type reasonably deal with types such as `color' that are defined in
wid-edit.el?