The user of the XDA Developers forum with the nickname maurydes released skin Deep Black for the shell EMUI 9. She brings a real black background in settings and the most standard applications smartphone Huawei Honor.
Have Huawei Mate Pro Mate 20 and 20 X is a function of the nominal Darken Colors Interface, which applies a dark theme to the entire OS, but other smart phones of the company this option to no.
Deep Black is designed to save power on AMOLED screens black pixels in these matrices are switched off, and therefore not wasting battery power.
Download Deep Black from the XDA Developers forum.