We could do like Textra, that lets the user change the icon color within the app
iOS seems posible now -> Telegram is offering it https://telegram.org/blog/contacts-local-groups#theme-picker-and-icon-style
For what it is worth I suggest not mixing color into the logo discussion. I purposefully didn’t change that when I presented my suggestion. I do think Delta Chat needs to update its color palette, too, though. So even if a hard relaunch to the projects visuals might be tempting I expect things to go slow here and step by step. Let colors be a separate discussion if possible.
One vote for purple.
reminds me of a notification management app I once used: Light Flow Pro
Blue for default, purple for unseen messages state?
violet hex #7F00FF
or this purple hex #702963