I believe that PO2 uses a more up to date version of PneumaticCraft than you might be used to - there are no more of any of the seeds - the different colours of plastic are generated instead using a Plastic Mixer, in which you put red, green and blue dyes (I think - might need to double check) and the uncoloured plastic, and this allows creation of all the different colours.
As far as I'm aware, this is standard in PnC now.
EDIT:
This covers the conversion of oil into liquid plastic, and MineMaarten mentions about using the plastic mixer to turn it into plastic.
I need to go look something up and may get back to you with further info as well. EDIT 2: The plastic mixer is also used for colouring too
Hope this helps! The seeds are still in NEI, but they aren't used in-game.