Often it's just the genetics of the drone fathers showing up. Mixed colors is more normal than all one color.
Look for bees wrestling at the entrance. If they are not, it probably isn't robbing. From the pic it looks like a small entrance, so robbing would be hard to get started.
Look for bees wrestling at the entrance. If they are not, it probably isn't robbing. From the pic it looks like a small entrance, so robbing would be hard to get started.