I just turned Brad Garlinghouse’s profile on Yahoo’s new social network, Yahoo Mash, peanut butter brown.

The site, which began an invitation only preview Friday, is quite an homage to Facebook, but it adds one significant new wrinkle: users can edit each other’s profiles, redecorating, changing information, and adding features. Think the Wikipedia version of a social network.

Since the site gives you the option to undo each change made to your profile, Mr. Garlinghouse can decide he doesn’t want everyone to associate him with peanut butter. (Mr. Garlinghouse, a Yahoo senior vice president, wrote a widely discussed memo complaining that Yahoo’s strategy was so broad and thin it was like spreading peanut butter on bread.) If you don’t like this game at all, you can change settings to allow just people marked as best friends or family to edit your profile, or you can keep the crayon box entirely to yourself.

Word of Mash leaked out earlier this week when a Yahoo employee invited my colleague Brad Stone to join before the trial was ready for the public.

The very first version of Mash can’t be accused of trying to do too many things at once. It is focused on goofy self expression and social interplay. The lead section is a series of fill-in-the-blank statements like “If I were an animal, I would be,” “The soundtrack of my life” and “My celebrity look-a-likes.”

There is also a little hand drawn figure that is modeled after a Tamagotchi or a Neopet: You, and your visitors, feed it pet it and it changes its expression.

Users can pick and choose from a range of modules to add to their pages. Some of the first ones, in fact are rather fun. There is a little game where you can play paddle ball with an image of Karl Marx. And the “Wheel of Lunch” is a nice use of Yahoo’s local database: type in your ZIP code and the type of food you want, and it will display a sort of Wheel of Fortune with spaces for local restaurants. Spin it to decide where to eat today.

Of course, Yahoo says it will allow outside developers to create modules soon, matching the hottest feature of Facebook.

Mash is trying very hard to be hip, particularly in its bountiful use of slang. E-mail notifications of new friends start “Woot.” A link that turns off the color and background of a page reads, “this is fugly.” And not only can you feed your pet, you can “snorgle” it.

For now, there are a lot of obvious features missing. There is no way to send a private message to users. There is no place to put useful information about yourself, such as where you went to school or where you work. There isn’t much emphasis on video or music.

And the site is for now largely divorced from the rest of Yahoo. The idea behind Yahoo’s last attempt at social networking—Yahoo 360—is that it pulled together everything users did on Yahoo: posting photos on Flickr, reviewing restaurants on Yahoo Local, bookmarking web sites on Del.icio.us, and so on. That wasn’t a bad idea, but the site was so utilitarian that no one used it.

Yahoo is trying (very very hard) to give Mash the irreverent feel of a Web 2.0 startup. If this actually catches on, and people do want to keep changing each other’s profiles, it will be easy to add more useful features later on.

[If you haven’t been invited by a current Mash user, you can’t see the site at all. But the blog by Will Aldrich, the head of the Mash team, is public.]

Update: Brad Garlinghouse’s profile is back to powder blue. And he wrote this in my “guestbook” the Mash equivalent of the Facebook “Wall”:

@Saul Hansell: hmmm, not so much on the brown (not even close to the refined hue of Jif!)… but the proposed contribution appreciated none the less

I do wonder whether this game is akin inviting your friends to cover your room with graffiti.