Well, as you probably already know, you can change the label color by right-clicking on the clip in the project panel and selecting ‘Label’.
However, clips already in the timeline will not update with the new color. You must either change the label color before placing the clip in the timeline, or ‘Replace With Clip’ after changing the label color.
You can also change the label color by right-clicking on the clip in the timeline, but this will not update in the project panel.
Same deal applies to changing clip names – something I find very annoying at times.