What layer is formed on Titanium when soaked in Hydrogen Peroxide?

A few pieces of TI-6AL -4V ELI ASTM F136 Titanium jewelry were left to soak in a small cup of 3% household Hydrogen Peroxide.


After about a week of soaking, all of the Titanium had acquired a smooth, dark grey/black coating. In the process, the Hydrogen Peroxide acquired a yellow tint.


I am familiar with Ti color anodizing, but this is a color that, as far as I know, is impossible to obtain with traditional anodizing methods. It more closely resembles industrial anodizing and the grey/silver color they obtain.


What process is taking place?


What is the grey coating made of?


Is it just oxidized titanium?


[![Grey Ti Jewelry](https://i.stack.imgur.com/qWlu4.jpg)](https://i.stack.imgur.com/qWlu4.jpg)


