[Enhancement] Different color for new mail to differentiate accounts

Submitted by Camaleon

Assigned to Florian Rivoal

Link to original bug (#16836)

Description

It would be a nice feature having the option to choose different icon colors for every account when new mail arrives. E.g., account1 → yellow envelope icon, account2 → blue envelope icon and so on.

It can be also used as a kind of identifier for group matching accounts. E.g, work accounts (account1, account2, account3) → red envelope, familiy accounts (account 4, account5) → green envelope icon and so on.

That way it's easier for the user to know what account (or what group of accounts) is the new mail coming from without needing to see the tooltip.

This feature would require some kind of icon rotation setting when checking every account to allow the user view the icon (e.g., 5 seconds by default, but configurable).

Now using 1.2.0 version.