"Red Seal" means you are a Journeyman. You have completed your apprenticeship and have written any exams required for qualification and professional status with the Provience or Country.
As Cook is what we call a "purple" trade you can choose whichever uniform you want. "Purple" is a term we use to describe certain trades that no matter what colour uniform you wear you still do the same job. Some trades such as Infantry, Armoured, MARS etc are specific to thier element so they have no choice. But Cook, RMS, Medic, etc have a choice. It doesn't mean any more money and just because you choose an Army uniform doesn'ty mean you'll never serve on a ship. Conversley if you wear a Navy uniform you may end up in a field unit.
The PLAR is the "Prior Learning Assesment Request" It's what we send to the Managing Authority of an occupation and they determine what level you are qualified to and what training you will have to complete. It all depends on education and qualifications.