100 Ideas: Litmus marking
This is idea No. 54 in the book!
For this you can use a visual colour scale (you might think of a litmus test colour chart or those colour swatches you see in DIY stores). Learners will then follow criteria you give them and select a colour level as their feedback to either themselves if self-marking or a peer if peer-marking.
A downloadable resource is available here to help you deliver this activity in your classroom.