Android 9.0 P comes with a special black screen mode. The mode developed for OLED and AMOLED displays will provide much more realistic colors. System colors that have been completely changed to black can be seen as an improved version of Always On.
Google can bring both black and sleep mode with the new version of Android.
If 'dark mode' is just gossip yet, phones with AMOLED and OLED screens will offer both more battery life and more realistic colors.
The new version of Android, expected to be correctly advertised in the summer months, is expected to start working towards the end of 2018.