This looks like a really fun challenge! I'm interested to try it myself. I hope you don't mind if I throw you some extra thoughts and ideas.
First, I just wanna say that I really like some of the challenges you've come up with. There are several that I haven't thought of or seen before, and I especially like the Independence Day challenge. Very creative stuff :)
I'm curious to know what determined which traits you gave to each color. Is it just that a particular trait has a certain kind of feel to it (gloomy = blue, for obvious reasons), or was there something else in mind? I just ask because I think each person might have a different interpretation of traits and what kind of color best matches it. For example, I personally feel the genius trait might fit better with the Indigo sim. Would it be okay for the player designing the sims to decide the traits themselves? Or maybe if you have your own specific ideas in mind for this challenge, you could write a list of potential traits for each color (maybe five or six) and the player can choose from those? For the most part, I agree with the traits you assigned already; I just feel that some of them are up for interpretation.
Regarding the challenges, there are a few that I think might be hard to control or monitor, only because there are so many sims. It's mostly the social challenges. I think the Meet and Greet challenge would be easy enough--send the sims to a public place and let them run around autonomously and then check their relationship tab at the end of the day. But I feel like the Speed Dating and WooHoo challenges would require a lot of controlling of the sims to make sure the conversations are headed in the romantic direction and then also to make sure the sims are in a good enough mood to make those interactions successful. Controlling the sims isn't a bad thing by any means, but with eight sims it might become tiresome to set up so many simultaneous romances. It might be a good idea to fine tune those challenges a bit. Maybe you could change it so that each contestant is allowed a certain amount of time with the romantic interest (say, two hours), and then you'd move onto the next contestant. And whoever has the highest romance bar or had the most WooHoo in that allotted time wins.
Just one more note on the challenges. The Drinking Game challenge may also be a bit hard to monitor, unless the player keeps a written tally of what number drink each sim is on while playing. Maybe you could play this challenge like the cooking and fitness challenges: just see which sim has the highest mixology skill at the end of the day.
I hope I haven't come across as critical here or anything. I really like your challenge idea; I just think it needs a few tweaks to be perfect. Great ideas though!