Yes, it did change its color! You start out with a normal card, and each time you complete one of these tasks clisted below, your card changes color, following the order listed below the below.
1: Beat Ghetis in battle
2: Collect all the props
3: Complete national pokedex
4: Raise the black and White levels of your Entree at the Entralink to 30 or more
5: Obtain trophies from both the Super Single Train and the Super Double Train in the battle subway.
These can go in any order, and you card changes color from
1: normal card, colored green
2: bronze card, colored purple
3: copper card, colored pink
4: siliver card, colored... well, silver.
5: gold card, colored gold.
6: black version, black card, colored black or
white version, white card, colored white.