Color gamut is going mainstream!
What does this mean for an average web use? More accurate color, more vibrant color, and particularly deep rich reds (think strawberries, bright red fabrics, sunsets, etc).
But also on many printers that can print far wider range of color than any picture a previous iPhone could generate using the “sRGB” color space (laughably called “sad RGB”).
For more, see iOS 10 Supports Color Spaces at diglloyd.com.