If you would like to write without a group, there are also weekly fantasy back stories on each of the characters. Go back and check the feed for @steemmonsters and you can see which one they are on for the week!
If you would like to write a template for the backstory of an actual color (splinter group), I supposed you could always start your own group and not allow anyone in. But it is not recommended. Just let @aggroed know!