There is a reason we anodize aluminium...you need that to protect it. The color is just a bonus. The anodizing it self is light grey, the color i just added later in the process. So what you want is "Nature Anodizing".
You need a mix of Sodium Hydroxide (NaOH) and water.
But if you are going to do this be CAREFUL!
I work with anodizing and have xp with this ****. Anodized alu are going a couple of minutes in this before anodizing. But why remove it? Anodizing makes the alu stronger.
Sorry for bad english...