Where did you get the info that this stamp will have a different appearance? Not what I heard, but then again, some of the info from the Austrian post offices were totally wrong, so maybe same here.
Read into it what you will, but this is from Andreas Petersson, who was part of the Cryptostamps project:

Rough translation: "the OCS stamps are much rarer than the red ones and should be part of a complete collection." You're right, he's not saying that they will have a different appearance. I guess we'll see.
Do you own all three? - I heard they were all bought by one person, lol.
Only one. I managed to snag it from opensea.
If you want to know the value, put it in auction and roll the advertisement roll for it so interested people will bid. Good luck.

My personal guess for value would be in the 1.5 - 4 BTC range. Possibly more. Have fun.

Thanks!! That'd be pretty sweet. I will sit on it until we at least can confirm the details of how the OCS stamps differ from the others, if at all.