As best as I understand it, to say that something is heraldic Proper is to say that it is an archetype, or a standard so that everyone knows what the object looks like in second. In other words, to say that I'm looking at an Heraldic Proper Apple, would be to say that it is round, red, with a brown stem, and green small leafs at the top -- everyone would draw the same shape and use the same colors.

So when Graham says that no one ever wanted to paint him "proper", in its heraldic sense, he meant, no one wanted to paint him for him.

I think "heraldic" terminology is used in identifying symbols within coat of arms, and identifying colors and things such as that. I'm sure it's a lot more complicated than this, but it's good enough for here.