I'm on a custom /e/ ROM based on Android 9. I found those notification settings for sound, vibrate, blinking light, showing the notification dot, but nothing about color.If you tap on the second button in the notification settings of the app, the right Android notification channel settings will be opened. How these settings look, depend on the Android version. Mostly you need to tap on the channel name before the switch for more options.
Ultimately though, I'm happy with the default yellow color. I just find it so strange for the LED to change colors mid-notification. Have you heard of this before?