I do keep some notes on lens coatings, some of which are included on my serial number page. For example, there is a note where the rear coating of the Nikkor-P 10.5cm changes to purple - although I neglected to add that previously it is amber - I probably should add it. I also note where SIC coating appears on some lenses, although that is not comprehensive - mostly on some AIS lenses where the change is obvious. So far I haven't bothered to find the same change in AF lenses, and in some cases the difference between older NIC and newer SIC coatings is not obvious so it is hard to tell.
Regarding lens coatings generally, as pluton said, coatings can appear quite different depending on the light source, colour perception, and also the viewing angle - multicoated lenses in particular can have very different colours when viewed from different angles. Much of my information comes from pictures on ebay where the quality of pictures varies greatly, so not easy to accurately compare lens coatings. Hopefully the pictures on my site give some indication of the colours, the pre-AI links to Richard de Stoutz's collection are particularly good, although the quality of my other pictures is mixed ...
