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I've been working with the fadings library in PGF and I was having trouble getting it working with externalize.

I finally figured out that it was working, but Apple's Preview does not display the fadings when externalized. I opened the PDF with Adobe Acrobat and the fadings worked fine.

Has anyone else come across this or know if it's a bug in PGF or Apple's Preview?

Here's an example using \includegraphics and \pgfuseimage:

% Three color triangles
\fill[green] (90:4) -- (210:4) -- (-30:4) -- cycle;
\fill[blue,path fading=west] (90:4) -- (210:4) -- (-30:4) -- cycle;
\fill[red,path fading=south] (90:4) -- (210:4) -- (-30:4) -- cycle;

Left is Adobe Acrobat, right is Apple Preview:

enter image description here

edit: Next is comparison between the above document in Preview and the externalized image also in Preview

enter image description here

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closed as off-topic by Joseph Wright Aug 10 '13 at 7:38

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This is fairly well known. Fadings do not work well with some pdf viewers. –  Jan Hlavacek Mar 9 '13 at 0:14
Thanks. However, I want to make clear that fadings does work in Preview, just not when externalized and re-imported. In fact, the standalone pdf will show up correctly in Preview and looks identical to the Acrobat rendering (I guess I should have included that comparison as well). –  Liam Mar 9 '13 at 18:52
[unrelated to question]: funny, I have just finished the documentation of pgfplots surface plots with explicitly given color (such as a surface patch with three corners and colors red, green, blue) pgfplots.sourceforge.net/pgfplots_unstable.pdf . The outcome of those patch shadings is identical to your overlaid fadings for this special case :) –  Christian Feuersänger Mar 9 '13 at 19:58
:) It is a nice looking triangle and a good addition to the pgfplots doc. I should have mentioned that the triangle I used is originally from texample.net/tikz/examples/rgb-triangle –  Liam Mar 9 '13 at 23:18
@Liam well, I added it to the pgfplots doc. However, the way pgfplots achieves this type of shading is substantially different. It would be done by means of \addplot coordinates { (90,4) [color=red] (210,4) [color=green] (-30,4) [color=blue] }; and a suitable set of options (taken from the manual). –  Christian Feuersänger Mar 10 '13 at 12:20