Possible Missing Color on Marshall Islands #627

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I am at a loss to explain what happened here.  Note the differences between the right-hand columns on the side-by-side images.

1.  Block in top margin:  T1 is yellow in one, white in the other.
2.  Man's coat in top stamp in column:  brown-tan in one, light purple in the other.
3.  Sky in bottom stamp in column:  much more brownish-gold in one than in the other.

However!  The color dots (not shown) in the top margin are precisely the same in both sheets; left to right, yellow, red, blue, black.  It's as if the printing failed only in the right-most column.  Any ideas?