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I had a problem with transparency, it wasn't show in pdf output. I have a similar problem with some tikz picture, that were not visualized well. I noticed that the problem with this two package (tcolorbox and tikz) was due to another package, I removed it and now the pdf works fine. The package was, weirdly, the "transparent" package. Can someone explain what was going on? I also have an other question, there's a difference from the package pgf and pgfplots? And from tikz to pgf?