Unfortunately, it looks like my friend found an extension of the problem from thread 901.

So, the issue is this:  he happens to be Red-Green color-blind.
So he can't tell which colors are chosen already in a private-game.
So when he accidentally chooses the same color as someone who is already in the game, it doesn't warn that he's choosing a color that is already used, it just ends up declining the game.
Only way to get him back in the game is to re-invite him until he chooses one that isn't used.

Two possible suggestions:
1) Warn that the color is already used, and give them the opportunity to join the game again.
2) Remove the "used" colors from the color options list.

He happens to be using (I'm sorry about this) IE6.
(If you've choosen not to support IE6, that's fine, ignore this issue, and he can deal.)
He's getting an upgraded computer for work in a week, at which point he'll have an updated IE so this issue might not be a problem for him anymore.

I'm just going to create the private games and add a message in each telling everyone what color he is supposed to choose (by the name) and then no one else will use that one.
So it's not a major issue for us, just wanted to let you know of what we'd found.

Scratch that, maybe it has nothing to do with color. He thought he was always choosing a color that was already picked, but apparently not. So this might just be an identical issue to thread 901.

Clicking Join = Decline.

Used colors should be removed from the color options list.

IE6 is not completely/very well supported and there have been quite a few unfixable bugs associated with it that tom has had to let live due to (I assume) complexity.

Is your friend a Premium member? If so, make sure he knows about clicking on a player's name in the player info table below the board in the Flash player (after a game has started) will highlight that player's territories, I could see this as being a huge help for those that are color blind.

Yep, IE6 breaks the join page I'm afraid so I'm pretty sure it's that. It's unsupported as if you can't join a game it does rather limit your interaction with the site ;) I'll add a message to the front page.

I dunno, we do have quite a bit of fun here on the forums.

Thanks for all the help. I've forwarded this info to him, so hopefully he'll get that new computer soon, and therefor IE6 will become a non-issue.

Then again, he was recently moved to Britain for work, and as such, I inherently distrust anything he says.

Yertle - He's not a Premium Member, but I have suggested to him that it might be worth it for him. His inability to see colors and WG's interface is one of the primary reasons why WG is better for us than WF.