Use themes

Theme files are placed in etc/themes.

Right click title bar -> Options.. -> Looks, select Theme, then Apply or Save.

If theme files are not in etc/themes, drag and drop theme files to Theme edit box, then Apply or Save.

Some Screenshots.

Download more theme files:

https://github.com/geoffstokes/base16-mintty

https://github.com/oumu/mintty-color-schemes

https://github.com/PhilipDaniels/mintty/tree/master/themes