Ubuntu – Vim in tmux display wrong colors

I have found the reason those escape appear by disabling everything in my .vimrc file and reenabling incrementally. For those people with the same problem, it is caused by the following setting in the .vimrc file:

set visualbell "Use a visual error indicator instead of a beep

Removing the above line fixed the problem.

Silly and logical, but well... There you have it.

I can help you solve the symptom, but not the root of the problem. The design of the prompt is configured in the variable PS1.

Outside tmux, this is the value:

$ echo ${PS1} # outside tmux
\[\e]0;\u@\h: \w\a\]${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$

This is the value inside tmux:

$ echo ${PS1} # outside tmux
${debian_chroot:+($debian_chroot)}\u@\h:\w\$

to fix the problem, you can run this command inside tmux, and the prompt will immediately look normal for the current window:

PS1='\[\e]0;\u@\h: \w\a\]${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

edit: I solved it by adding the following line to ~/.tmux.conf

set -g default-terminal "screen-256color"