Nick Keppol from MartianCraft goes deep on the new icons in Mac OS X Yosemite:

When 10.10 ships this fall, your users will expect your icons to feel at home in the new system. Rather than critique the icons, I’m going to dissect the icon system and focus on the small details that will help you make icons that look great in Yosemite.

Over the past few weeks I’ve spent a lot of time trying to understand the new system and taking note of the visual language. This is what I’ve uncovered.

Really interesting stuff.