Krita v3 Linux Mint/Ubuntu 16.04

serialband: that does install v3, but not the latest just simply 3.0

Natty Greg: this does not install v3 I still only see 2.9.7

True but after you want to sudo update
then sudo upgrade and it will upgrade everything that needs to be upgraded

paulq@Mint-PC ~ $ sudo apt update
Ign:1 http://dl.google.com/linux/chrome/deb stable InRelease
Ign:2 http://packages.linuxmint.com serena InRelease                          
Hit:3 http://repo.steampowered.com/steam precise InRelease                    
Hit:4 http://packages.linuxmint.com serena Release                            
Hit:5 http://dl.google.com/linux/chrome/deb stable Release                    
Hit:8 http://archive.canonical.com/ubuntu xenial InRelease                    
Get:9 http://security.ubuntu.com/ubuntu xenial-security InRelease [102 kB]    
Hit:10 http://ppa.launchpad.net/gns3/ppa/ubuntu xenial InRelease              
Hit:11 http://archive.ubuntu.com/ubuntu xenial InRelease                      
Get:12 http://archive.ubuntu.com/ubuntu xenial-updates InRelease [102 kB]      
Hit:13 http://ppa.launchpad.net/graphics-drivers/ppa/ubuntu xenial InRelease  
Hit:14 http://ppa.launchpad.net/kubuntu-ppa/backports/ubuntu xenial InRelease  
Hit:15 http://ppa.launchpad.net/libreoffice/ppa/ubuntu xenial InRelease        
Hit:16 http://ppa.launchpad.net/otto-kesselgulasch/gimp/ubuntu xenial InRelease
Get:17 http://archive.ubuntu.com/ubuntu xenial-backports InRelease [102 kB]
Hit:18 http://ppa.launchpad.net/paul-climbing/ppa/ubuntu xenial InRelease
Hit:19 http://ppa.launchpad.net/stebbins/handbrake-releases/ubuntu xenial InRelease
Hit:20 http://ppa.launchpad.net/wine/wine-builds/ubuntu xenial InRelease
Hit:21 http://ppa.launchpad.net/wireshark-dev/stable/ubuntu xenial InRelease
Fetched 306 kB in 2s (121 kB/s)
Reading package lists... Done
Building dependency tree      
Reading state information... Done
All packages are up to date.
paulq@Mint-PC ~ $ sudo apt upgrade
Reading package lists... Done
Building dependency tree      
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
paulq@Mint-PC ~ $ krita --version
Legacy integer arithmetics implementation
Qt: 4.8.7
KDE Development Platform: 4.14.22
Krita: 2.9.7

That means you have the most stable release above that is nightly or snap shot, so once become stable it should upgrade

You had answers to your question, so to delete without issuing points is unfair

Your right, the question was answered in a way. The closure was not based on your helpfulness in trying you were great.