I just made a black and white marble swirl soap - I think if I had just left it as is the way I glopped it in without stirring it and then running a chopstick through - it would have moo mooed -
So I reckon (taking into account that I am mainly a MP crafter and have only just started CP)
1. combine oils and lye water, bring to thin trace - like crepe batter consistency.
2. Take some of the thinly traced mixture out and mix in black oxide with a bit of charcoal powder.
3. Bring the uncoloured thin trace to full trace and do the same with black mixture -
4. then glop one white, one black, one white, one black, one white, one black (for bigger moos - use bigger spoon).
5. When you're done glopping, pick up the mould and whack it gently on the counter to get it to all sort of mush together.
Dont really know if it will work out without swirling - but that's how I would imagine it could be done.
I have done a similar sort of thing with MP soap - but I waited for the soap to thicken up a bit before super speedily glopping. It came out alright but I had to keep remelting the soap mix. and I topped up with clear base.