Favicons are not generated as proposed

Nextcloud 13RC3, debian 8.10, Apache 2.4.10, PHP 5.6.33

I try to enable favicons. I followed the advice on
and installed libmagickcore-6.q16-2-extra and php5-imagick

Since I set my NC instance color in Theming to green I expected that I now should see green favicons. I don’t. What am I missing? There’s no documentation, no log entry, … (No, I don’t want to read the source.)

Any hint appreciated, like a “how I did it”-blog or a recent howto.