I saw a couple of these posted here... you are given a specific color palette and have to create something with it. I like art challenges - they keep me going. The idea seems to have originated on DeviantArt. Or possibly tumblr. I don't use either of those. Is there a group for it here? If not, would anyone else be interested in joining one? It doesn't seem like it'd be too tough to set up and keep going - unlike trade groups there's nothing to keep track of, people participate or don't without letting anyone down. Having a collection of all the different art and artists would be really neat though - a challenge is only half as fun if you can't see how others responded to it!
If anyone is still lost, here's an example: http://magicalzombie.deviantart.com/art/30-Day-Palette-Challenge-211435339
There is a group on DA that puts out a new palette each month and collects the art for everyone in the group to see. That's what I would like to see and/or do!