It would be neat to have favorites/bookmarks in different colors. I often find that I want to bookmark messages for very different reasons.
- Answer later. I can't write the answer right now, don't have the time.
- Read later. When I have time. Read one time probably.
- Reference material.
- Soft flag. Benefit of a doubt for new members. The quality of the question leaves a few things to be desired. E.g. schematic/diagram is needed, otherwise the question is unclear. The O.P. was prompted to post the schematic. Revisit later.
The feel and UX could be not much different from starring messages in gmail.
According to this post on meta.SE, the idea of more elaborate bookmarks has been going around.