Water droplets act like tiny reflective/refractive mirrors, so they pick up whatever surrounds them. In your setup, the black plastic around the bowl is being reflected in the droplet, which is why you see black instead of mostly white.

To make the droplets look whiter:

• Replace or cover the black material with white material.
• Surround the droplet area with a larger white surface so the droplet “sees” mostly white.
• A tent/sphere-style diffuser with a lens hole can help create more even white reflections.
• Try the flash without the diffuser as well, since changing the apparent light source can affect the reflections.

To control color intentionally:

• Put colored gels or transparent colored plastic over the flash.
• You can also vary flash placement and distance to change how sharp or soft the reflections appear.

In short: the droplet color is mainly determined by what it reflects, not just the background directly behind it. If you want white droplets, make the environment around them predominantly white.