...with black slacks is any shoe color other than black acceptable? and... What slacks option does one have when wearing ox blood shoes/belt?
Black is the easiest choice for accessorizing black slacks, but not the only choice. In Europe"”especially Italy"”it's not uncommon for men to wear brown shoes with black slacks. I see no reason why you can't do it with oxblood as well. (I've worn different colors with black, too; blue, green, etc. I was not, however, accessorizing a suit.) Oxblood works with navy, charcoal, beige. With brown, you just have to be sure the shades aren't so close that they clash.