Does anyone know of a definitive site with information about the lens coatings used by different manufacturers?

I have a variety of lenses, and they have a variety of lens coatings..
Older lenses have yellow or blue coatings, while newer lenses have purple or green.
Was the color just a gimmik? Why did they not have perfectly clear coatings?

Are some coatings better than others?
Which manufacturers skimped on their coatings or had uncoated internal elements?