Try these add-ons:

https://addons.thunderbird.net/en-us/thunderbird/addon/phoenity-icons/

https://addons.thunderbird.net/en-us/thunderbird/addon/colored-folders/

https://addons.thunderbird.net/en-us/thunderbird/addon/account-colors/

https://addons.thunderbird.net/en-us/thunderbird/addon/account-colors/

In the next release of TB, 78, folder colors are built in.

Thanks, I'm not looking for addons, I only ask hoping that it will be improved in the next versions.

I don't think adding more color is on the agenda for the next release - quite the opposite - and most current add-ons will not be compatible. if you want to customize the interface with userChrome.css, there are many examples posted in this forum.

Ok. Developers can put this idea into future plans.

how i can talk or write at the developers?

You would need to post a request for enhancement in the Bugzilla forum. But don't hold your breath, they are helpful when it comes to an enhancement in functionality or a bug. I asked previously if they could at least keep the previous blue style as a theme option, but it was not supported by the devs involved.

I would normally post a link to bugzilla, but at the moment it is totally impossible in the forum. They have applied some filters to stop spammers etc and rendered that kind of help as not allowed. Hopefully, they will get their heads together soon and fix this issue.

Besides Bugzilla, there is a site devoted to user-interface issues:

https://thunderbird.topicbox.com/groups/ux

Managed to locate some info on bugzilla as reference, but make sure you use the one for Thunderbird.

File a bug report or feature request for Mozilla products