I love pinned tabs but is anyone peeved when they have lots of tabs open having everything grey? Favicons are so small that they need some colour to be able to differentiate between them at a quick glance and navigate to. I'm sure Apple could highlight the current tab another way. Put in your bug reports in!
What Apple need to do is something similar to what internet explorer does. IE is the only browser natively tagging different set of site using different color. This feature is super useful, and I really like it.