force tmux to use 256 colors by adding the -2 flag

modules/tmux/init.zsh

@@ -30,7 +30,7 @@ if [[ -z "$TMUX" ]] && ( \
     tmux set-option -g destroy-unattached off &> /dev/null
 
     # Create a new session.
-    tmux new-session -d -s "$tmux_session"
+    tmux -2 new-session -d -s "$tmux_session"
 
     # Disable the destruction of the new, unattached session.
     tmux set-option -t "$tmux_session" destroy-unattached off &> /dev/null
@@ -40,7 +40,7 @@ if [[ -z "$TMUX" ]] && ( \
     tmux set-option -g destroy-unattached on &> /dev/null
   fi
 
-  exec tmux new-session -t "$tmux_session"
+  exec tmux -2 new-session -t "$tmux_session"
 fi
 
 #