Soon as I saw the picture this was exactly my guess.

I only nly soap occasionally, once a year at most, 30 or so 3lb batches. So I only use very very simple recipes for 2 very simple reasons I am lazy, and it's soap. None of these fancy schmancy micas and dyes and butters and creams and honeys and embeds and piping. Just lard, lye, and water, and half the batches have fragrances. The only thing remotely considerable as a colorant that I use would be the couple fragrance oils that have vanillin.

I have white bars, cream bars, tan bars, and even outright brown bars. The fanciest bars I make turn out just like OP's pictures because every once in a great while I get fancy enough to split batch the fragrance throw at two different concentrations, layer the two concentrations and wire stir for almost exactly this marbled effect after the vanillin cures.

When I'm actually possessed by the spirit to be artsy enough to do this I split the soap 50/50. In one portion I'll throw 1 or 2 parts of the fragrance oil, and the other 4 or 5 parts. It's subtle compared to traditional midas and colorants but nice enough for me when I'm feeling artsy fartsy.