Hi Ian, great update. You're doing wonders in that small model.
For the pc12 look apart from the misterkit you have some other colors close to that.
From humbrol you have Matt Dark Earth 29, but could be a little dark for scale purpose, so have a look to Brick Red 70, if you like Vallejo you may have a look at Chocolate Brown 872 or Orange Brown 981 or with Tamiya Flat Earth XF52.
So have a look on those and see wich best fits the model.
For the blue paint you may go Misterkit or Humbrol Aircrat Blue 65 (maybe to dark?) or Duck Egg Blue 23 (imho i fing it quite good), from Vallejo you have Sky Blue 961 wich i find a little to dark (but again this is me

and from Tamiya you have XF23 Light Blue.
I'm affraid that i contributed only to confuse you... or maibe not. Just want you to see what you have around.
Cheers