After finding out the available colorscheme of VIM in your machine, the next step is to set a colorscheme.
Let’s assume that you have the following colorschemes available
Now to set the colorscheme to blue
$ vim filename.txt
Enter the following in Normal mode
As you can see the syntax for setting a colorscheme is
Note that if you enter a scheme name which is not available, you will get the following error
:colorscheme abc E185: Cannot find color scheme abc
You can change a colorscheme using the same command.
Note that when you change a colorscheme by the above method, it is for a particular session only. Once you exit, you will lose the change. Read How to change a VIM colorschme permanently?