From Gemini onwards Recovery Ship cachets were dominated by Morris Beck's printed cachets and the Morris Beck
designed Navy Rubber Stamp Cachets (NRSC). For the Primary Recovery Ship (PRS) and some Secondary Recovery Ships
(SRS) the NRSCs were often done in two or more coloured inks with the most common being maroon and black.
The question arises as to how these inks were applied. There are two general possibilities (of course some
combination of the two is also possible).
a) One colour of ink was applied to all covers until the ink pad started to give less ink. Then a new colour was used. We know this method was used for at least one mission (and probably many more if not most) thanks to a cover discover by Ray Cartier (bottom left in below picture). This cover has definite traces of both maroon and black ink which shows up better with the actual cover.
Click on picture for a larger version
b) A second possibility exists because Beck provided two rubber stamps to each ship1. Thus
it would be possible (especially during later missions where the number of covers being cacheted and postmark became
extremely large) for the Postal Clerk to use one rubber stamp with one colour ink pad while an assistant used the
second rubber stamp with a different colour ink pad. This would certainly be an efficient use of labour. Unfortunately,
unless there was some minor different between the two rubber stamps, there is no way to tell whether this method
was ever used.
While Maroon & Black are the most common colours, other colours were occassionally used as shown below.
Only seen on GT-2 & GT-8 cachets
Not seen on PRS covers
1) U.S. Space Cover Collecting Handbook, Ray Cartier et. al. (2011), page 109
2) The USS Ellison from GT-3 represents a special case. See my article on these covers.