The documentation says:
The following environment variables are set for Linux containers:
TERM:xtermif the container is allocated a pseudo-TTY
But apparently it supports 256 colors, or not? So I can probably set TERM=xterm-256color (granted that ncurses is installed, and the value exists in the terminfo database). Any other values?
UPD xterm-256color seems to work. You might want to use it to tell applications that 256 colors are available. Some applications might get away without this.