This is a quick post on how to cross-grade from regular kali linux to kali-purple:

1) make sure you have the correct kali sources for rolling-releases

cat /etc/apt/sources.list 
# See https://www.kali.org/docs/general-use/kali-linux-sources-list-repositories/ 
deb http://http.kali.org/kali kali-rolling main contrib non-free non-free-firmware 
# Additional line for source packages 
# deb-src http://http.kali.org/kali kali-rolling main contrib non-free non-free-firmware

2) update your repos, and install latest versions of packages:

sudo apt update
sudo apt upgrade -y
sudo apt autoremove

3) install the kali purple tools:

sudo apt install kali-tools-identify kali-tools-protect kali-tools-detect kali-tools-respond kali-tools-recover -y

4) install the purple theme:

sudo apt install kali-themes-purple -y

5) re-install the menu to get the tools added

sudo apt install --reinstall kali-menu

6) install the wallpapers

sudo apt -y install kali-wallpapers-legacy

You can now set the wallpaper, and the theme for your desktop environment :)