Now this is a most interesting Soviet stamp. Issued in 1968, I recently found that I have a version with what looks to me like two missing colours.
This is the normal stamp:
But what I find interesting is that the scan of the error stamp shows a significant amount of yellow and a smaller amount of pale green:
Yet, to the naked eye, this stamp is simply black and violet-grey. The yellow cannot be seen at all, even when the stamp is being looked at closely with a magnifying glass, while the pale green looks more like bone-white.
Does anyone know what's going on here?