My phone has just completed the latest update.
I did have my work shifts in the calendar app. They were all colour coded so that I could see at a glance what was what.
The theme is now grey and I can't see what shift is when unless I select the day itself. The is no option that I can find to switch it back.
How is this an upgrade or as actually helpful in any way at all. This needs to be changed back.
I've seen a similar post to yours from another member who isn't in favour of the more muted colours either @Sg1044 on the Samsung Calendar.
Have you considered using another calendar app in the interim.
Daily Driver > Samsung Galaxy s²³ Ultra 512Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "