Almost all PDFs use the CMYK or RGB colour profiles.
However, Apple devices (iPad/iPhone) only support Apple RGB colour profile. This means that your PDF colour profile may need converting to the correct type. If not, the colour of your digital publication colours on Apple devices may appear different to the source PDF.
Here is a side-by -ide comparison of an publication viewed on a iPad - one PDF has not been converted to Apple RGB whereas other one has.
. 
RGB and CMYK Colour Profile
There are two ways to alter the colour profile of a PDF.
The first is to edit the file when exporting to PDF using InDesign. The second method is to use Adobe Acrobat.
You can click the following links to download the profiles for use in Acrobat that will be discussed in this guide:
Acrobat 9 Profile Acrobat 10 Profile
How to import the profile
First you must ensure that Print Production is available under Tools. To do this, click the drop down panel just under the Comment section and select the Print Production option:
To then import the profile, select:
Tools > Print Production > Pre-flight > Options > Import Profile
How to use profile
Now that the profile has been imported it, will appear under the Imported Profiles subheading - simply double-click the profile and select a save location for your newly converted PDF file.
Benefits of using Pre-flight
Adobe Acrobat has a standard tool that allows you to alter the colour profile of a PDF.
We recommend not using this as the tool seems to increase the file size of the PDF, whereas the above profile reduces the file size by a considerable amount which means less for the end user to download.