I worry about the typical acrylic baseball holders--you are still exposed to risks from UV light (including from your light bulbs), humidity, etc. Gaylord has boxes that are good for long-term storage (see link below) and you can display the balls in acrylic as needed.
http://www.gaylord.com/adblock.asp?abid=15754
Leather is not naturally white, so all baseballs are in the process of returning to their original color. The best you can do is to slow the process.