You need a CUSTOM ROM.
It supports Android 6, 7.0 and 7.1 / Google Pixel / OxygenOS 4 / LineageOS / OMS +

– Keyboard AOSP & Google (dark & light)
– Android System
– Calculator
– Contacts AOSP
– Contacts Google
– Documents
– Gmail
-Instagram
– Play Store
– Google Play services
– Google+
– Keep
– Media Storage
– Android Messages
– AOSP Messaging
– Package installer AOSP & Google
– Settings
– System UI
– System UI Naviagiton
You need the substratum theme engine app to apply the theme!

The notification colors are partially set within the frameworks and it’s not possible to theme the frameworks in all Android versions. This is why the notifications are white on some ROMs. You can read more about this in the FAQs.
Theme App

Substratum Theme Engine app (Use this app to apply