Just an idea here. The problem is not with the color but the reflectivity of the metal. If you were able to modify the reflectivity without modifying the color, perhaps you'd have a solution. Maybe that could be accomplished by imparting a texture to the metal. Maybe sanding or beating it with a textured surface of some kind. I don't know -- grasping at straws here. The thing is, aluminum oxidizes pretty quickly, and the more texture you apply, the more of it has contact with the air, so you may get a slight color shift. But aluminum oxide is white, whereas pure aluminum is silver, so I'm guessing there wouldn't be a significant color shift. Worth a try? Anodizing the aluminum just right may be just the ticket.