New tmux session to split window into two panes. Want to set TERM=screen-256color on both panes, but the script only sets it on pane :1 and not also pane :0. I am trying to use sync panes, but not seeming to work.

gistfile1.sh

txsi() {
    local session=foo

    tmux new-session -d -s "$session"
    tmux select-window -t "$session":0
    tmux split-window -h
    tmxu select-pane -t 0
    tmux synchronize-panes on
    tmux send-keys "export TERM=screen-256color" C-m
    tmux synchronize-panes off
    tmxu select-pane -t 1
    tmux resize-pane -x 21
    tmxu select-pane -t 0
    tmux -2 attach-session -t "$session"
}