I generally don't look at the item, but I've seen what you are talking about.

The various highlights correspond to the various Conditions. There is Normal (no highlight), Good, Excellent, and Poor.

Normal is, well, normal. Nothing special happens.
Good, two things can happen. One, you can pop a Tricks of the Trade (if you have that skill available, level 15 ALC cross class skill) to get up to 20 CP back (its always 20, unless you're under 20 from full). Two, any Quality adding action (any Touch, or Byregot's Blessing) will add 50% more. If you're working Progress, nothing special happens.
Excellent does two things. One, any Quality adding action adds quadruple the normal Quality. Two, it automatically makes the immediately following Condition to be Poor.
Poor can ONLY follow immediately after Excellent. Any Quality adding action only adds half the normal Quality.


I want to say a brighter White glow is Good, a lot of rainbow colors is Excellent, and the Black/Purple is Poor. But, I'm not 100% positive on that.