Yes, believe it or not, it isn't a 3c 1861, and it's not pink, but it is a stamp from 1861, specifically August 1861, and specifically one of the "August Issues" or "Premieres Gravures", Scott #62B on cover.
I saw this last night when I was at the Nashville Stamp Club meeting, looking at
ebay on my phone, and saw no bids, with a $250 start. I was the only bidder, and won it for $250.
I've been pricing this stamp for several years now-- it's a very difficult issue-- expensive and scarce, and I've never seen a sound one for under $300-- and probably haven't seen one under $500. AND, I've never seen one on cover on eBay-- reading in The Chronicle a few months back, I think that there is actually a census of 62B covers, and I wonder if this one is included.
I asked the dealer to send the cover directly to Weiss, and he emailed me today and said that it definitely looked like a 62B-- so it looks like I've got 2 "August Issues" now (I bought the 3c a couple of years ago). Very excited......here is a pic:

The 62B (Type I) is fairly easy to distinguish from a #68 (Type II)-- the 3 things that I look for are:
On the top above the design, there is only one scroll-- in the 68, there has been an extra one added.
Around the stars, all of the shading is dark-- where it is all light in the 68.
Below the stars, in the 62B, there is not a thick re-engraved line at the border of the stars area, and in the 68, the line has been re-engraved and is thick.
So, when I have it in hand, I'll scan a larger picture and show the differences.
Just wanted to gloat- Ray