More than one company made playfields for WMS. Even though they used pantone colors, they didn't always match 100% from manufacturer to manufacturer.
You can compare 2 Creature playfields, side by side, here:
The 'hot pink' ones in this case were screened by Sun Process (noted by a SP by the part # under the apron), and the regular pink ones were screened by Lenc Smith, noted by LS under the apron by the part #.
There's a lot of good reading here, discussing different companies screening playfields etc.
http://www.flippers.be/pinball_playfields.html
