Antoine Fourrière wrote on Sat, Jan 18, 2003 11:00 PM UTC:
The eye of the Jack is the symmetrical square (e.g. z4 and i4, or d7 and
e7, are each other's eye). A square and its eye are not on the same
color.
Hence, when the Jack goes as a mirror Wazir (say, from z4 to h4, i3, i5 or
j4), it is colorbound, while when it goes as a mirror Firz (say, from z4
to h3, h5, j3 or j5), it is color-changing.