Advice needed: Any ideas on how I might approach creating objects like these marbles? I have tried Vellum Softbodies, Flip Sims, and Vellum Cloth but nothing seems to give me good results. Could be my inexperience, of course. Any suggestions for how I might approach this would be greatly appreciated!

My initial thought: two or three tubes - one for each colour - each randomly offset from the origin. Add a generous splash of 'mountain' SOP, followed by 'Bend' SOP in twist mode. Convert to vdb and smooth as required. Convert back to polys.

There's probably a bunch of really cool ways to simulate that. It would be funny to see an over complicated fluid sim video that could achieve it, but kinda like Mike_A suggests some standard modeling might also get you there fine. My materials and rendering in houdini are pretty bad right now and im still learning myself but I wanted to see what this would look like, its just a bezier curve with a sweep. If you were more precise with everything it would probably look pretty close to your reference. I'm not sure the best way to get the colors on the helixs like the reference, like how the inner and outer faces are different and some have clear glass running down the centers/etc