I just installed Oracle Linux 7.3 on Virtual Box. I had installed KDE too.
I chose 'KDE Plasma Workspace' at login window. Although I got KDE desktop, It is still the red one like GNOME. Screenshot shown below
I want it to be like below (this screenshot is from RHEL 7.2 though )
Another sample of what I am looking for :
In the video link provided below, from 9th minute onwards , you could see three virtualbox VMs .
Host OS is MacOS. Guest VMs are Oracle Linux 7.X . You could see the Oracle Penguin Icon on top left corner , near 'Application' drop down menu. The icon is small though.
I am looking for these KDE desktops
https://www.youtube.com/watch?v=PzzjAb1pc-E