The driver update, which was first noticed and reported by the German publication Mac & I, enables support for 10-bit color depth within OSX El Capitan on certain higher resolution Macs, including the latest Retina iMacs, the Mac Pro, and some 15-inch Macbook Pros. The significance of 10-bit color is that, once fully supported by the display hardware and software you're using, you will be able to see significantly more detail in the subtle gradations between colors.

To help explain and demonstrate why 10-bit matters so much, here's a brief excerpt from David Torcivia's excellent article about what to look for when purchasing a new monitor for color grading:

8bit means a video codec or display is only capable of 16.7 million colors. That sounds like a lot until you compare it to the 1.07 billion colors a 10bit panel (or codec) is capable of. It's quickly apparent why a 10bit panel is so superior to 8bit. This is especially true when working in codecs that are 10bit (or greater). An 8bit monitor would be incapable of displaying all the colors!

A result of the fewer colors can be the introduction of banding in your images.

8 bit vs 10 bit display

The downside here is that you likely won't be working in 10-bit color on your Mac any time soon. Because 10-bit has to be supported in not only the hardware and software that you're using, but also in your media, chances are that this update won't mean much to you right now unless you have an external 10-bit display, work exclusively in the native Photos OSX app (the only place besides Finder in which 10-bit support is enabled at the moment), and have some high bit-depth media to work with.

With all of that said, now that OSX offers 10-bit compatibility, we should start seeing software developers — Adobe and Blackmagic are at the top of that wish list — incorporating native 10-bit support into their products. Once that happens, you should be able to take full advantage of your higher bit depth media, provided that you have a 10-bit display as well. This could also mean that future generation of Apple displays (all of which are traditionally 8-bit) could make the jump into 10-bit territory.

Source: Mac & I