I think black boots are fine, actually, since outfield they will
quickly be covered in mud, and in camp they are easy to kiwi black
in about 30 seconds and also polished (if necessary). Can you
imagine trying to kiwi brown boots to a uniform colour? Definitely
not as easy as black kiwi.
The idea I believe, is not to kiwi them at all, especially if
the boots are tan or green! Haven't heard of green kiwi, lol...
But in any case, you can always have a second black pair for
parade and drill... after all in the old days (as in my time cira
2004-2006) we were issued gortex combat boots for outfield and
leather ones for drill and parade. Then apparently the SAF decided
to cut costs and issued leather ones across the board for the
recruits, only allowing them to switch if they went to combat
vocations of something like that.