11.86; XeTeX engine doesn't use Emacs foreground color

Any simple LaTeX document containing a preview-able part can
reproduce this.

Steps to reproduce:

1. Set Emacs foreground color to non-black and background
   accordingly.

2. Open some LaTeX file, with some math formula.

3. Set variable TeX-engine to 'xetex, and TeX-PDF-mode to t,
   press C-c C-p C-d.  (Maybe twice is needed)

OK, and you'll see the preview's foreground color is black, not
the Emacs foreground.

Emacs  : GNU Emacs 24.0.93.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.2.3)
 of 2012-02-25 on XeCycle
Package: 11.86

current state:
==============
(setq
 AUCTeX-version "11.86"
 LaTeX-command-style '(("" "%(PDF)%(latex) %S%(PDFout)"))
 image-types '(svg imagemagick png gif tiff jpeg xpm postscript xbm pbm)
 preview-image-type 'png
 preview-image-creators '((dvipng
                           (open preview-gs-open preview-dvipng-process-setup)