In the v11 Beta, when you choose an account colour, it replaces the account avatar.
I understand it is just meant to apply a colour to the window headers when you send a message/open a message thread, not change the avatar.
When you select a colour in your account and the Avatar also changes to that colour, then “click the Avatar again” and “reselect your Avatar”.
That will then have you account colour and original Avatar intact. Then save accounts.
Great, thanks for the workaround!