I dont really see a need for this “feature” as it is quite easy to do with “rules”.
Create a rule:
- After message has been received
- received using *your email address*
- set categories *newcategory*
You can either show “category” in the column display of mail screens or under the “appearance -> lists” settings, tick or untick “Use color of category as text color”
There you go… Simply to implement with the existing application. I have it set up for different colours already and it works a charm!!!