I usually use TeXShop in Mac to make a document, and I had a problem with figures: The color and fonts are weird when I open the PDF file with Adobe Acrobat. I found a lot of questions and answers about this problem in Google and here including this, and basically the answer is simply adding the following line in the preamble.
\pdfpageattr{/Group <</S /Transparency /I true /CS /DeviceRGB>>}
It worked, and everything is fine. But I do not know the meaning of the above line. I just want to know what it means and why we should insert it in the preamble. Thank you.