Techniques for forming a metal oxide from a metal substrate are disclosed. In some embodiments, the metal oxide can have an optical path difference between about 300 nm to about 1000 nm. The variations in optical path difference can impart the metal oxide to correspond to a range of pre-defined colors. In some embodiments, the optical path difference can impart the metal oxide to have an oxide color that is substantially similar to a color of a housing of a portable electronic device. In some embodiments, the metal oxide can be electrically conductive and the metal oxide can be utilized as an electrical contact of an electronic device to transmit and receive power and data from another electronic device.