Question

Do diamagnetic ferrofluids exist?

Answer 1

Diamagnetic materials are repelled by a magnetic field; an applied magnetic .... These are attracted to field maxima, which do not exist in free space. Diamagnets

Answer 2

You can try a simple experiment and hold a magnet to your liquids. They may have slight diamagnetism, already, it depends on the chemical composition. It's unlikely that you will see anything, though. I also don't think that your customers would appreciate 10% bismuth in their models, or so... graphite, maybe, but that might give you hell with the optics.