Marbled bath bombs

[toyah999]

Hi, I've made a few batches of plain coloured bath bombs that I'm happy with but I would love to jazz them up a bit. I've tried putting baking stars on top which look cute but I want to try marble them. I've seen a few that are marbled and they look great. Does anyone know how to do this? I assume I half my batch and colour both differently and then just kinda alternate a bit of each colour in the mould or do you mix both colours in the bowl before moulding? Thanks.