Metallic paint is free as others have stated expect for the premium colours of the range. The grant should not make a difference as if you were paying the AP yourself you wouldn’t pay for the paint. It is motability policy and is stated somewhere.
The only thing I’d wonder is you said optional extras. Your only allowed 50% of the value of the grant you were offered to add extras or improve on what they offered.
Current Car
KIA Sportage GT Line Mhev
Previous Cars
Peugeot 5008 Allure Premium
VW Touran SEL
Citreon C4 Picasso