[dvipdfmx] bug with inclusion of a PNG

[Paulo Ney de Souza]

I have (a couple) of PNG images with a background color of, for example,
RGB(80,64,83), that when placed on a page of the same background color with
`graphicx` -- they show a distinct tonality against the background -- which
is of the same color, when run under XeLaTeX. There are no problems under
pdfLaTeX or LuaLaTeX.

----
\documentclass{report}

\usepackage{xcolor}
\definecolor{bgcolor}{RGB}{80,64,83}

\usepackage{graphicx}
\pagestyle{empty}

\begin{document}

\pagecolor{bgcolor}
\includegraphics[width=0.5\textwidth]{A.png}
\quad
\includegraphics[width=0.5\textwidth]{B.png}

\medskip

\includegraphics[width=0.5\textwidth]{A-gimp.png}
\quad
\includegraphics[width=0.5\textwidth]{B-gimp.png}

\end{document}
---

Checking the colors in the included files one can see they have changed
from (80,64,83) to (71,56,74) in the first two included images.

Just opening the images on `GIMP` and exporting it as-is with the default
choices, fixes everything and the new inclusion now gets the exact color
they were set to begin with, the same as the background, as shown below
(second line).

Looking at the PDF, Ultike Fischer (at TeXHax) traced it to a problem with
dvipdfmx that, she determined, uses the wrong color space (CalRGB) for the
first two images and DeviceRGB for the last two.

What is that XeTeX needs from the PNG's to preserve their color when
included in a page?

For experimentation here are all files attached.

Paulo Ney
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