If you include a picture within a pdf document and view it with the Adobe Reader you may notice a change of color under certain circumstances. Let’s test this png file:

This short example will be enough to produce a pdf by pdflatex:

\documentclass[a4paper,10pt]{article}
\usepackage{graphicx}
\begin{document}
\includegraphics{test}
\end{document}

You may compile by yourself or look at the pdf output. Here’s a screenshot of the Adobe Reader:

Nice blue color, but not the original one. Compare this color with a screenshot of the open source pdf viewer Evince:

Because most people use the freely available Adobe Reader it may be necessary to fix this issue. I found a solution by converting the color mode from RGB to an indexed palette using the freely available open source software GIMP. Here is the changed png file, and here the pdf file, finally the screenshot:

Using GIMP it’s possible to automate the conversion by GIMP’s batch mode using the procedure gimp-image-convert-indexed.

This topic was discussed in the LaTeX Community Forum.