Easy achievement that took under 5 minutes to unlock.
*The other solution above is sufficiently explanatory
but here is another, to add context for those who have never looked at the game before, and want to get this done ASAP.*
1. From the Main Menu go down and select CUSTOMIZE
2. Go down and select CHARACTER
3. Now select any character with A (
) and then press A again to enter the color customization menu
4. Hit right on the analog stick or d-pad to change a color. Hit A to finish, and then go up on the analog stick an A again to save your changes.
5. Hit B again to return to the character menu.
6. Repeat this with 9 other characters-- the achievement will pop when exiting the Color menu on the final character