Perhaps that's why nobody manufactures any white SMB's.
Actually, Carter does. I have one made by them that is white, with a dive flag printed on one side of it. It's vinyl coated and waterproof and can be used as a dry bag for clothes, as a lift bag, or as a dive flag/smb.
But from a visibility standpoint, I much prefer my orange 80lb halcyon bag with SOLAS tape on it.