Do you mean the people in cycling colours?
Yes
They aren't just admin if they have the rainbow player. It might just be a private add-on.And according to MediaFire, the add-on is called Client_RainbowMe.zip. I don't recommend it. It simply is show-off, makes lag, etc.
Yea just a stupid addon that lags up every thing
It doesn't really cause lag it's just damn stupid and several mods have been made to kick people with it.