Are you referring to background color (CSS background-color) or font colour (CSS color)
The "Background -> Fill Style -> color" is just that ...... Background Fill
The font color can also be changed on hover by adjusting the color under the Typography tab.
Or do you mean to have the button's background change on hover then you would do this by choosing "Hover"
and changing the background fill in the inspector.
If you mean have a color fill in the normal state and then a gradient or image fill in the hover state then you cannot do this using the above technique ... you will have to code in the CSS in the Head HTML