Q: upgrading operating system

Hello we have an old Power Mac G5 Quad 64bit desktop computer with a 10.4.11 operating system. We are just now looking into upgrading. I was told by Apple support they no longer carry the 10.5 disk and that I would need to look to ebay to purchase the disk. I found the Lepard installation disk on ebay and I'm needing help on which to purchase.

Apple Mac OS X Leopard ...  I have found 2 boxes that have an X on the front with a background color of either red or purple/blue. I don't know if the background color means anything but if they do I don't want to purchase the wrong one.

Mac OS X 10.5 Leopard Server 10 Client Full Retail Install Package DVD Disc .... also has an X with a green background, the box says it's a server, not sure if I need to purchase this also along with the purple one or red one.

Any help is appreciated, thank you.