What is "Proper" in the Heraldic sense?

As best as I understand it, "heraldic" terminology is used in identifying symbols within coat of arms, and identifying colors and things such as that.

To say that something is heraldic Proper is to say that it is an archetype, so everyone knows what the object looks like.
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.