Please see attached.
What do the different colored skill stars mean?
What are the two different prices below each item?
Thanks.

The stars just indicate how good someone is at a given talent. They go up in half stars a single red half stars means they are not very good and 6 whole stars means you have mastered the talent.
As for the different money values I can't remember 100% and I'm not at a computer where I can check the game but I believe the top higher value is how much you can buy a given item for and the lower bottom value is how much you can sell the item for.

For the 2 prices - I think one is the purchase price, one is the sale price

Sorry to say that I am still confused not about the stars, but the use of colors: neutral, red, and green. I understand that the number of the stars represents a skills modifier coefficient. But I don't understand what additional semantics the colors convey. Or do they perhaps convey the source of a bonus or malus?
Thanks.

Looking at the screenshot you added, I am pretty sure it means that Informer Archibald Goldholme:
* Has a Negotiation skill of 3 stars, but is using an item which gives him an extra star (4 stars total)
* Has a Handicraft skill of 3 stars
* Has a Stealth skill which has been reduced to 1/2 star
* Has a Combat skill which has been reduced to 1/2 star
* Has a Rhetoric skill of 3 stars, but is using an item which gives him an extra 1/2 star (3 1/2 stars total)
The reduced skills might be because of an item he has used (increase negotiation at the expense of combat), or because of an item someone has used against him.
I am not sure about the red stars... it could also mean it's been reduced from 0.5 to 0, but I don't think that's likely?

I thought the green and red stars indicated how far along they were to improving that ability. However that was just an assumption, as later on I noticed those stars going gold, and further green and red stars appearing.

Here is another color coded question. What does the gold portion of the effect bar mean? (see attached)
Thanks.

My guess would be potential. However I think it's better if you play through, and sus it out. It won't take long. My first game has been in london on piss easy, and I've got to grips with most of it (still working out how to actually hurt my competitors beyond a mild annoyance). Just experiment and find out.

The green is your current effect of those bonuses. The yellow is a decrease in the effect because your house has not been renovated in a while. The black bar shows how much you could improve your house.