When you use Acrobat Reader to open a PDF file that was exported by Adobe Illustrator the PDF will be displayed in the SPOT colors internally used as green.
To render a realistic preview of your design do the following.
Use Adobe Acrobat Pro to open the PDF file.
Go to
Go to the [Protect & Standardize] section and click on [Add] below the [Print Production] tool. [Print Production] will now be added to your standard [Tools Pane].
Click on [Print Production] to open the tool and click on [Output Preview] on the right side.
Uncheck the [Spot Plates].