Soybean flower colors are usually white or purple. One plant will have flowers of the same color (i.e., all white or all purple).
Flower color is controlled by a single gene. Soybean is a self-pollinated plant and does not require pollinators such as bees. As a result, flower color has no effect on yield.
For more information on this and other topics related to soybean production, contact your state extension specialist or your local extension educator/agent.
Following is the link to the soybean extension specialists: state extension soybean specialist.