/sci/ - Science & Math

hey /sci/ ,
I don't know where else to ask this, so here goes
>friend and i bullshitting one day
>some how his gf comes up
>gf has metal earrings that she can take to this place and some how they have a machine that changes the color of the metal
>she can change them from pink to purple to blue etc
>fascinated by this
>spend hours googling for color changing earrings
>just get endless tarnished silver tarnished gold results
>start looking metals and other materials that can change colors with current
does anyone have any clue what kind of metal can change its color and retain the new color if given a current?
was my friend mistaken and its some kind of polymer?
I'm interested in knowing about color adaptive materials