I recently managed to get a number of proofs in an auction. I quite like proof printings, especially if they're different from the end result. Proof printings are usually made to see how designs work out, how colours work out, etc. So they are an important part of the story of how stamps are made.
This one here is a proof printing of the "Van Konijnenburg" definitives, so named after its designer.
And here's the end result.
As you can see, the lighter colours chosen in the end make for a better stamp and so does the thicker lettering. And notice that they've shortened the country's name and all. So these are very interesting copies of proofs indeed and I'm mighty chuffed that I was able to lay my hands on them!