I don't think anyone knows so I'm bumping if that's OK?

I would think they would be white unless they got crossed with another color

I hope you'll try it and post back here with your results.

When I was a kid my mom grew hyacinth bean that had white flowers and brown seeds. This year is the first time for me growing hyacinth bean with white flowers and white seeds. Two years ago I didn't even know there was a white seed variety. If the plant wasn't vining together with a colored flower variety, it's likely that the seeds would be of a white flower variety with genetically mixed seed colors.