No colors in zsh for first tmux session

When I start a new tmux session (macOS 11.5.1, iTerm2 3.4.10, zsh 5.8, tmux 3.2a) with tmux new, my terminal has no colors, it just displays everything in grey tones. But when creating a new window or split window, the colors are there right from the beginning. Also, when I already started a session and I create another one with tmux new the colors also work from the beginning. When I close every session, and open another one, it displays everything in grey tones again. This is my .tmux.conf, maybe there is something wrong with it?

set -g @plugin 'tmux-plugins/tpm'
set -g @plugin 'tmux-plugins/tmux-sensible'
set -g @plugin 'dracula/tmux'

set -g @dracula-show-fahrenheit false
set -g @dracula-show-powerline true
set -g @dracula-show-flags true
set -g @dracula-day-month true
set -g @dracula-show-network false
set -g @dracula-show-battery false
set -g @dracula-show-time false
set -g @dracula-show-location true
set -g @dracula-show-flags true
set -g @dracula-show-left-icon smiley

set-window-option -g mode-keys vi
setw -g mode-keys vi
bind-key / copy-mode \; send-key ?
bind-key -T copy-mode-vi Escape send -X cancel

bind-key -T copy-mode-vi 'v' send -X begin-selection
bind-key -T copy-mode-vi 'y' send -X copy-pipe "reattach-to-user-namespace pbcopy"

# remap prefix from 'C-b' to 'C-a'
unbind C-b
set-option -g prefix C-a
bind-key C-a send-prefix
bind a send-prefix

bind-key C-a last-window

bind -n C-k send-keys -R \; clear-history \; send-keys "Enter"
set-option -g mouse on

# change order of windows by pressing Ctrl-Shift-Direction Key
bind-key -n C-S-Left swap-window -t -1\; select-window -t 0
bind-key -n C-S-Right swap-window -t +1\; select-window -t +1

# join panes
bind-key j command-prompt -p "join pane from:"  "join-pane -s '%%'"
bind-key s command-prompt -p "send pane to:"  "join-pane -t '%%'"

# stay in the same directory when creating panes and windows
bind '%' split-window -h -c '#{pane_current_path}'  # Split panes horizontal
bind '"' split-window -v -c '#{pane_current_path}'  # Split panes vertically
bind c new-window -c '#{pane_current_path}' # Create new window

run -b '~/.tmux/plugins/tpm/tpm'