Kali is a Linux distribution created for ethical hacking and penetration testing and is commonly used by researchers and red teamers to perform security tests against an organization.
As most people are used to seeing Windows and macOS devices being used, it may look suspicious to see a user running Kali Linux with its distinctive dragon logo and a Linux environment in an office lobby or other public setting. With this in mind, in Kali Linux 2019.4 the developers created a new 'Undercover' mode that will make the desktop look similar to Windows 10 in order to draw less suspicion.
Whilst it actually looks quite good they could have also just changed the background image and basic theme... Most Windows users would not recognise a Linux desktop unless it clearly showed a Linux logo or branding (my mom never knew the difference, and she used an actual Linux Mint desktop).
Kali Linux 2019.4 was released last week and with it comes an 'Undercover' mode that can be used to quickly make the Kali desktop look like Windows 10.