I have used Dubbins for over 15 years for all my Doc's.  Black, Brown, doesn't matter.  Dubbins keeps the leather subtle and water resistant.  For the steel toe Doc's, when they get hit on the toe cap, the leather simply "gives way" and does not rip.  I use this on my Doc industrial Ironbridge Black boots with the internal D03 Met Guard as well as my slip on Doc Industrial Icon Steel Toe Gaucho Boots.  It does turn the brown a little darker, but that fades within a day or so.  I have always used Dubbins for all my Docs, even on my little toddlers brown cowboy boots.  Protect your leather and it will last a lifetime.  You just spent $120+ on a pair of quality boots, buy the leather care product and take care of your investment.  This is not a shine product, it is meant to keep the leather soft and protected.