I was wondering this too and it seems like they only change when you change the look of ALL of your icons. Hard press to get the screen layout options to appear. Then use the paint brush and select “Customize”. You’ll then be able to choose between default, dark, clear or tinted.
That said if anyone knows of a way to change just the appearance of Mail, Settings, Safari and App Store, I’d love to hear about it. That’s all i wanted was to change them. Not the theme for all icons.
