Colorized index for notes

### What
In panel of notes, A patch of coloring on left side will make the notes more organized. I uses simple note to keep multiple notes from different domains.

### Why
Colors will provide a strong visual indication and a user can get hold of the notes he would need in more easier way.

No file, test, or entry point is named. Start by locating the notes panel UI and reviewing how notes are represented, then clarify the color assignment and placement with maintainers; done means the panel shows a clear left-side color cue without disrupting note browsing.

Written by the indexing model from the issue text.