I have been faced with the same problem for a while now and I would like to know what's wrong and how to fix this.
I am trying to make the most realistic product render possible and this issue is preventing me to make it look as good as it should.
When rendering a white product, sometimes light bounces from it to another part, or simply reflect itself.
When the product is purely white, it seems like colors ADDS up, the reflection actually make it whiter that it is supposed to be.
I am using 3Ds Max 2014 with mental ray and arch and design materials.