Examples of the covering materials used for the slipcase.

1. From a 1958 2nd State slipcase.  Paper with a finish similar to a fine textured leather.
2. From a 1960 4th State slipcase.  Linson with an embossed texture intended to be reminiscent of linen.
3. From a 1963 5th State slipcase.  Paper with a finish similar to a coarse textured leather.
4. From a 1963 5th State slipcase.  Paper with a finish similar to a coarse textured leather.

The colour difference between examples 3 and 4 may be in part a result of fading, but there does appear to be a real difference as well.  Both contain the same impressions of the three volumes - FR 13th 1963, TT 9th 1962 and RK 9th 1962.

Another slipcase, containing all 1962 impressions, appears to be a shade of grey somewhere in between.  Therefore it seems likely that the shade varied slightly from batch to batch.