I think I misunderstood your question. I thought you meant that you didn't know which Vifm pane you were in.
This is probably not the right place to discuss Tmux, but here are some values from my config file that you can look into. I use these to help distinguish between active and inactive Tmux panes:
# Set background color of inactive/active panes
set -g window-style 'bg=colour234'
set -g window-active-style 'bg=terminal'
# Status bar color for active window
set-window-option -g window-status-current-style \
fg=brightred,bg='colour236',bright
# Border color for active pane
set -g pane-active-border-style fg='brightred'
# Displays arrows pointing to the current pane. Available since v3.3
set -g pane-border-indicators both