I use ICSx5 in combination with DAVx5 to synchronize calendar links from Nextcloud onto my phone. DAVx5 and Nextcloud correctly display the colors of the calendars that I set in my NextCloud settings (blue and yellow respectively).
On initial sync, ICSx5 also gets these same colors, and the color is also correctly shown in my calendar App, Etar.
After a while, though, ICSx5 (and therefore also Etar) suddenly switches the color to dark green and violet for the two calendars. Setting the color back manually to the color from NextCloud or even a different color doesn’t matter, after around half a day it always goes back to dark green and violet for the two calendars.
One of the two calendars in question is public, so I can share the link (https://calendar.google.com/calendar/ical/2904.cc_lq509kkank97fftfkjm3gmbq70%40group.calendar.google.com/public/basic.ics). The other calendar is private, so I will not share it here.
Device Info: Huawei Honor 9
App Info: ICSx5 1.8.9, DAVx5 3.3.1
Both DAVx5 an ICSx5 are whitelisted in the battery settings to be able to run in the background.