To change the background colors of your party members, and the colors of the dots that appear on the map to represent your party members, you need to press X to open the menu, then choose Misc., then choose Tactics. There you can move your cursor to the right side and select the color that you want to change.

To use a treasure map, go to Items in the menu and choose Treasure Maps. Then select the map and choose "go treasure-hunting." If you are outside of a town, you will see the treasure map in the top screen. For help finding the location, use the Grotto Map Hex Code Finder. When you get to the spot marked with an X on the map, a ! will appear and you can press A to make the grotto entrance appear. Use the Grotto Map Viewer to see the full map of the grotto.