Trainer Card has changed color. What this means?
Your Trainer card's color has changed, in XY there are 4 color (3 stages) and for each color you must do 3 things that are:
• Defeat the Elite Four
• Complete Kalos Pokédex Dex
• Battle through one of the Battle Maison facilities and defeat the leader at the 50th streak
You have Silver and the last is Gold. So depending on what you need, if you complete those 3 things your Trainer Card will be gold color.
The 4 colors are Green then Blue, Silver/Black and Gold. In other generations are 5 colors.
Although the Trainer stars and color changes are for the most part aesthetic, certain NPCs like the Pokémon Center Nurse change their greetings to acknowledge the player's achievement of obtaining 4 or 5 stars.
Sources - Experience from my Black 2 + Serebii and Bulbapedia
Hope this helps.