Pantone inks are inks that are used in Printing mainly garfield, really unless you have a deep interest in print media then I would steer clear of their uses. Rest assured that it has no meaning in relation to the increasing image size.
As for your cirlce dillemma do the following:
Press Q on the keyboard to enable quick mask, with a paintbrush cover over the white highlight in the centre of coloured circle.
Press Q again and you will see marching ants appear around the white highlight, this means that it is now protected.
Choose, Select>Colour Range. You will notice that an eyedropper tool is now selected. Click on the white border that you want to get rid of, and press delete.
You may have to play around with the sliders in the Colour Range to get the desired result - but its only by experimenting and going wrong a few times that you will learn anything
good luck
