Reading the comment from Trevor about the rare stamps of this set, I put together some material about the 250 ruble stamp.
Here are the main shades of the basic stamp as I found in my collection. The 3rd and 4th stamp are repeated.
The first three stamps are the most common shades you can find. The last two ones are somewhat more special.
It becomes more obvious if you look at the detail. If you compare the sickle shading you can see that within the dark blue shades the lines are unclean and a lot of ink was used. The other two stamps look much cleaner and the single shading lines can clearly be seen. Additionally the shade is more off from the dark blue. A greenish-grey and a grey lilac shade.
The first stamp. Dark blue. A bit too much ink. Unclean appearance. There are even spots of ink on the border.
The second stamp. Almost the same shade but not as dark or intensive. Same unclean appearance.
The third stamp. Same dark blue shade, but cleaner appearance. The shading lines in the sickle can be spotted.
The fourth stamp. In comparison an extremely clean appearance. Ink seems to be greenish-grey.
The fifth stamp. Again very clean appearance but the ink is more light bluish, perhaps ultramarine.
In comparison here is the artist proof of this stamp. It is not a clear black, more a dark brown. The artist proofs feature all stamps of the set in this color.
And at last the version on chalky paper. A very bright appearance and a bit unclean appearance – probably due to the paper not able to absorb the ink.
Overprints can be found only on the main dark blue shades, with the exception of the light blue (ultramarine) shade. Here some examples.
The 15 Goldkopeck overprint on the most common dark blue shade.
The 1 Goldkopeck overprint. In contrast to the 15 Goldkopeck overprint this one can be found on perforated stamps.
The 1 Goldkopeck overprint on a light blue stamp. I am unsure if this is the original color of the stamp. It looks like it saw heavy usage (on letter or in water or in sun light or all together).
The 1 Goldkopeck handscript overprint on the main shade.
And the same overprint on the rare light shade. Overprint and stamp are genuine and each alone already rare – the combination probably even more.
Some questions remain. What is the background of the “clean” shades? Early printings, when the stone were fresh? A batch of special good ink, that did not last very long and later cheap ink was used? The cheap ink had not so good characteristics and clean prints were no longer possible?
What is the story of the handscript overprint on the light shade? Was it made later from remnants?