WordPress seems to have a rather simple visual editor. It is limited with some frequently used button, such as Bold, Italic, Link and etc. Some user find it hard to change text color, or finding a heading to use.
WordPress visual editor has some useful advance buttons that are hidden by default. A quick click of button will unveil all those hidden buttons. Here is the magic button:
It used to be called “Kitchen Sink”, since 3.9 update, it was renamed to “Toolbar Toggle” (Make more sense).