According to the HTML spec , the theme-color meta tag is valid. Google has stated that Chrome for Android supports it from v39 onwards, and I believe Brave for Android, Vivaldi, and Opera (even on desktop, for those last two) also support it. Is there a comprehensive list of browser support?
theme-color is supported only by Chrome mobile browsers, version 67 (May '18) onwards, all latest samsung browsers and Vivaldi browser.
None of the other major phone browsers support this.
Source: caniuse.com - theme-color
On desktop, only Vivaldi browser supports it : Vivaldi blog
Note: All though Chrome mobile browser supports theme-colors, they don't work on desktop apps anymore when viewing a PWA.