[O] Bug: Latex preview fg color w/tikz (known problem, fix suggested) [9.1.9 (release_9.1.9-65-g5e4542 @ /home/carlos/local/stow/emacs-26/share/emacs/26.1.90/lisp/org/)]

[Carlos Pita]

Hi, I know this problem has been reported in the past ([1], [2]). The
second link provides a hint to a solution that I've developed
further. The underlying problem is (from dvipng man page):

 -fg color_spec Choose foreground color for the images. This option will
     be ignored if there is a foreground color \special in the DVI. The
     color spec should be in TeX color \special syntax, e.g., 'rgb 1.0
     0.0 0.0'.

So the current approach to latex fragment previewing is broken as far as
any latex package indirectly uses xcolor to set background or foreground
color, tikz being a prominent example.

As a more robust solution, I suggest to explicitly set the colors in the
tex fragment for the preview instead of passing them as arguments to
dvipng. This can be done easily:

...
\usepackage{xcolor}
...
\begin{document}
  \definecolor{bg}{rgb}{0,0,0}
  \definecolor{fg}{rgb}{1,1,1}
  \color{fg}
  \pagecolor{bg}
...

Where fg and bg might be replaced by randomly generated string or
whatever you see fit to prevent name clashes.

Notice that the syntax for rgb color is the same than the one for dvipng
so it shouldn't be much of a refactoring.

Best regards
--
Carlos

---

[1] https://lists.gnu.org/archive/html/emacs-orgmode/2010-01/msg00635.html

[2] https://lists.gnu.org/archive/html/emacs-orgmode/2012-05/msg00865.html