I asked a long time if there was a way for a user to tell if I have read a given book I might have found in a search.  I was told something about looking at the stars which, to me, show the average rating of the book.  

But look now, I am thinking if the stars come up blue, that means I havent rated the book.  If they come up yellow, it means I have rated the book. Can anyone confirm?  thanks

Yes, yellow is your own rating. Blue is unrated by you. But each person only sees their own yellow ratings .... I can't tell what your book ratings are, even if i look at your bookshelf. i only see my own. The only place where you can see someone else's ratings is if they write a review, their rating of the book is shown at the top of the review.

Keep in mind your rating only shows up on that specific version of the book that you rated.  So if I think I've read the book, I'll do a search for all versions and check them all.

And once you've rated a book by clicking on the stars, the book will be added to your Books I've Read list, so if you are looking at the listing, you'll see that it's on your BIR.

I always stick a personal note on every book I've read. That way, it's easily visible when I run a search & when I scroll through someones's bookshelf.

Of course, if you are trying to make sure you don't order it again, etc. you probably need to go to every version of the book in the system and add the note. This would be true of reviews too, as a review is only added to the one you have open, they don't link to all versions.